diff --git a/TESTING.md b/TESTING.md
index 1b56e9b..ffcfde2 100644
--- a/TESTING.md
+++ b/TESTING.md
@@ -3844,6 +3844,105 @@ The browser server writes its logs into `<server root>/logs`
 times, rotated copies, a link (POSIX) and a user's `.bak`, and roll the copies over; no
 test reads or deletes a real log folder.
 
+`tests/browser/system-diagnostics-concept.spec.mjs` compares the section and its log
+cleanup review with the concept (dark and light, 1600x1100 and 390x844, no page scroll;
+both selects show their whole option at 320 wide). The fixture's `{mode: "concept"}` seed
+reproduces the concept's Logs sample: only its four buffer lines, a 1.4 MB active log with
+three rotated copies and console logging off, so those values are compared as the concept
+prints them. `mapDiagnosticsConcept` applies only D109 and D110, and `mapCleanupConcept`
+D100 (the shared `mapPlanConcept`) with D109's rule for this plan (no backup box, "Not
+needed: no library record changes", "Listed files"). The mutation check asserts that the
+unmapped difference is exactly the deviated paths. The comparison found that the Database
+line read `database_info.size_bytes`, a key the report does not have, so it always said
+"0 bytes"; it reads `database_size_bytes`, the key `get_database_info()` returns.
+
+### Legacy System capability coverage
+
+Every System capability of the legacy admin and gallery pages has an owner (#249 System
+S12, #329). Status is `covered` (a native control replaces it), `kept in legacy` (it stays
+on the legacy page, which keeps working) or `approved removal` (a ruling retired it). Native
+control is `` `<section>` · <role> · "<accessible name>" ``, `<section>` a System hash id
+and `<role>` one of button, combobox, switch, slider, spinbutton, textbox, group, status or
+term, followed by ` · in "<row title>"` when several rows of the section share the name.
+Every `covered` row names one, except the rows in `CONTROL_EXEMPTIONS`
+(`tools/vendor/legacy-coverage.mjs`), each with its reason: today only "Gallery per-image
+auto-tag / review", which the Images selection bar owns, not a System section. A row that
+is not `covered` names none (`—`). Test is the exact title of a test that runs, then its
+file. Anchors are line numbers on `main` at this PR.
+
+`tests/vendor/legacy-coverage.test.mjs` fails on a row with any of these problems:
+- no owner, or a status outside the three;
+- a malformed Native control cell;
+- a covered row without a control (unless exempt), or a control on a row that is not
+  covered;
+- a test title its file does not declare: `test(` or `it(` (`.only` and `.slow` count),
+  or a `def test_` at function or method indentation;
+- a title whose test is only declared with `.skip`, `.fixme` or `.fail`.
+
+A title that appears only in a comment or a Python docstring does not count. CI running
+those tests green is what proves them. `every covered legacy System capability has its
+native control` (workspace-system.spec) opens each covered row's section and finds the
+control by role and accessible name, inside its row when the cell names one. The shared
+"Review plan" of the per-operation review row and the Sources "Refresh" of the monitoring
+list stay unscoped: any row's control proves them.
+
+| Capability | Legacy anchor | Owner | Status | Native control | Test |
+| --- | --- | --- | --- | --- | --- |
+| Image scan directories add/remove | `admin.html:377–390`; `admin.js:200,1273–1323` | S4 Sources | covered | `sources` · button · "+ Add source" | Add source validates on the server, then marks the host draft dirty; Save persists (workspace-system-sources.spec.mjs) |
+| Currently monitoring list + Refresh | `admin.html:392–400`; `admin.js:1032` | S4 Sources | covered | `sources` · button · "Refresh" | watching only with a live observer; restart pending otherwise (workspace-system-sources.spec.mjs) |
+| Monitoring enabled | `py/config.py:212,248` | S4 Sources | covered | `sources` · switch · "Watch for new outputs" | Watch for new outputs saves monitoring_enabled; a restart applies it (workspace-system-sources.spec.mjs) |
+| Search results auto-hide `result_timeout` | `admin.html:407–412` | S3 Appearance | covered | `appearance` · spinbutton · "Node search auto-hide (seconds)" | host fields round-trip through /settings with revision (workspace-system.spec.mjs) |
+| Web UI display mode | `admin.html:414–422` | S3 Appearance | covered | `appearance` · combobox · "Open from ComfyUI" | host fields round-trip through /settings with revision (workspace-system.spec.mjs) |
+| Infinite scrolling default | `admin.html:424–430`; `admin.js:689–727` | Legacy prompt list (README continuous browsing); read-only in the report | kept in legacy | — | shouldLoadMore asks for the next page only near the bottom with pages left (list-state.test.js) |
+| Worker threads | `admin.html:437–445` | S4 Sources | covered | `sources` · slider · "Worker threads" | worker range max is cpu_count (workspace-system-sources.spec.mjs) |
+| LoraManager badge, enable, path, trigger words, CivitAI key, clear key | `admin.html:448–490`; `admin.js:1052–1156` | S10 Integrations | covered | `integrations` · switch · "LoraManager integration" | LoRA rows show detected / enabled / cache-loaded separately (workspace-system-integrations.spec.mjs) |
+| LoRA data import with progress | `admin.html:492–498,517–541`; `admin.js:1157` | S10 Integrations | covered | `integrations` · button · "Review import" | Review import shows replacement, blocked items and network effects with the backup box; Start opens the job (D107) (workspace-system-integrations.spec.mjs) |
+| Statistics | `admin.html:159`; `admin.js:1627` | S2 Overview | covered | `overview` · button · "Explore" | statistics dialog lists runs by category and library totals (workspace-system.spec.mjs) |
+| Export components JSON `/export` | `admin.html:163`; `admin.js:1607`; `py/api/prompts.py:238` | S9 Backup & export | covered | `backups` · button · "Export all prompts JSON" | Export JSON downloads /library/export; secondary buttons download all prompts (/export) and /pairs/export (D103) (workspace-system-backups.spec.mjs) |
+| Saved pairs export | `py/api/pairs.py:84` | S9 Backup & export | covered | `backups` · button · "Export saved pairs JSON" | Export JSON downloads /library/export; secondary buttons download all prompts (/export) and /pairs/export (D103) (workspace-system-backups.spec.mjs) |
+| Library export | `py/api/library.py:223` | S9 Backup & export | covered | `backups` · button · "Export JSON" | Export JSON downloads /library/export; secondary buttons download all prompts (/export) and /pairs/export (D103) (workspace-system-backups.spec.mjs) |
+| Diagnostics run | `admin.html:171,659`; `admin.js:1984` | S12 Diagnostics | covered | `diagnostics` · button · "Run checks" | Run checks opens the shared Health report (workspace-system-diagnostics.spec.mjs) |
+| Synthetic image-link test | `admin.html:662`; `admin.js:2101` | S12 Diagnostics | covered | `diagnostics` · button · "Create test link…" | Create test link confirms first and names the prompt (workspace-system-diagnostics.spec.mjs) |
+| Maintenance cleanup_duplicates, vacuum, cleanup_orphaned_images, prune_orphaned_prompts | `admin.html:692–748`; `admin.js:1834` | S6/S7 Maintenance | covered | `maintenance` · button · "Review plan" · in "Duplicate prompt text" | Apply reviewed operation closes, toasts, opens the job in Activity (workspace-system-maintenance.spec.mjs) |
+| Maintenance check_hash_duplicates, check_consistency | `admin.html:692–748`; `admin.js:1834` | S2 Health report (Maintenance notice, D123) | covered | `maintenance` · button · "Run health checks" | Run health checks opens Health report and updates metric 4 (workspace-system.spec.mjs) |
+| Maintenance statistics (database info) | `admin.html:692–748`; `admin.js:1834` | S12 Diagnostics | covered | `diagnostics` · term · "Database" | meta-grid shows real database and source status, the pinned Viewer.js version and the host renderers (workspace-system-diagnostics.spec.mjs) |
+| Maintenance select all / clear all / run | `admin.html:754–762`; `admin.js:1822–1833` | S7 per-operation review | covered | `maintenance` · button · "Review plan" | plan dialog shows the server's scope, protected, backup policy and media lines with the backup box (D100); Cancel writes nothing (workspace-system-maintenance.spec.mjs) |
+| Prompt cleanup `/cleanup` | `py/api/admin.py:620` | S6/S7 Maintenance | covered | `maintenance` · button · "Review plan" · in "Duplicate prompt text" | test_duplicate_prompts_plan_counts_the_legacy_groups (test_maintenance_plans.py) |
+| Database backup | `admin.html:179,824`; `admin.js:2139,2454` | S9 Backup & export | covered | `backups` · button · "Back up" | Back up downloads through the api client and revokes the object URL (D103) (workspace-system-backups.spec.mjs) |
+| Restore from file | `admin.html:183,616–642`; `admin.js:2177–2248` | S8/S9 Backup & export | covered | `backups` · button · "Review restore…" | Review restore stages the chosen file and shows the real summary with the backup box (D105) (workspace-system-backups.spec.mjs) |
+| Metadata scan with progress, cancel, pill | `admin.html:187,805–865`; `admin.js:2336–2500` | S4 Sources | covered | `sources` · button · "Review scan" | Review scan opens the shared Review metadata scan with all sources (workspace-system-sources.spec.mjs) |
+| Rescan-required notice + dismiss | `admin.html:1367–1410`; `admin.js:991–1011` | S4 Sources | covered | `sources` · button · "Later" | notice Later persists the 3.2.0 dismissal (pm_update_notice_dismissed) without scanning (workspace-system-sources.spec.mjs) |
+| View logs with level and limit | `admin.html:195,885–907,974`; `admin.js:2579–2641` | S12 Logs | covered | `diagnostics` · combobox · "Level" | level filter is minimum-level over all six choices (workspace-system-diagnostics.spec.mjs) |
+| Log statistics | `admin.html:921–941`; `admin.js:2512` | S12 Logs | covered | `diagnostics` · status · "Log statistics" | log statistics show entries, errors, warnings, files and size (workspace-system-diagnostics.spec.mjs) |
+| Log files list and download | `admin.html:910,982–985`; `admin.js:2545,2642,2679` | S12 Logs | covered | `diagnostics` · button · "Download log" | each listed file downloads by its returned name and a link has no Download (workspace-system-diagnostics.spec.mjs) |
+| Clear/truncate logs | `admin.html:915`; `admin.js:2704` | S12 Logs | covered | `diagnostics` · button · "Clear all logs…" | Clear all logs states both counts, confirms first and reads everything again (workspace-system-diagnostics.spec.mjs) |
+| Rotated-log cleanup (new, #329) | — | S12 Logs | covered | `diagnostics` · button · "Review log cleanup" | Review log cleanup lists only rotated copies and keeps the rest (workspace-system-diagnostics.spec.mjs) |
+| Set log level (incl. CRITICAL), console logging | `admin.html:948–966`; `admin.js:2530,2729` | S12 Logs | covered | `diagnostics` · combobox · "Runtime log level" | runtime level (including CRITICAL) and console logging save and say they apply until the server restarts (workspace-system-diagnostics.spec.mjs) |
+| Log file_logging / max_file_size / backup_count / buffer_size | `py/api/logging_routes.py:56,285–299` | S12 Logs (read-only) | covered | `diagnostics` · group · "Log files & retention" | each listed file downloads by its returned name and a link has no Download (workspace-system-diagnostics.spec.mjs) |
+| Auto-tag model list with status | `admin.html:1095–1148`; `admin.js:3641` | S11 Auto-tagging | covered | `tagging` · combobox · "Tagging model" | model options are the four real engines with size and the description shows live status (workspace-system-tagging.spec.mjs) |
+| Auto-tag model download | `admin.html:1413–1438`; `admin.js:3680–3747`; `gallery.js:3412` | S11 Auto-tagging | covered | `tagging` · button · "Download" | Download starts the job and Activity shows it without Cancel (workspace-system-tagging.spec.mjs) |
+| Unload model | `gallery.js:3480` | S11 Auto-tagging | covered | `tagging` · button · "Unload" | Unload is enabled only while a model is loaded, and a held gate's refusal names the operation (workspace-system-tagging.spec.mjs) |
+| Tag template, WD14 thresholds, already-tagged mode | `admin.html:1150–1198`; `admin.js:3748` | S11 Auto-tagging | covered | `tagging` · combobox · "Existing tags" | defaults save through Save preferences and the Tag image dialog uses them (workspace-system-tagging.spec.mjs) |
+| Batch auto-tag output images | `admin.html:191,1210,1279–1318`; `admin.js:3748–3840` | S11 Auto-tagging | covered | `tagging` · button · "Review" | Tag output images reviews the scope and starts a batch job (workspace-system-tagging.spec.mjs) |
+| Batch review loop | `admin.html:1206,1218–1364`; `admin.js:3841–4172` | S11 + image-tagging plan | covered | `tagging` · button · "Preview tagging review" | Preview tagging review opens the Tag image dialog for the selected image (workspace-system-tagging.spec.mjs) |
+| Gallery per-image auto-tag / review | `gallery.html:601,605`; `gallery.js:3506,3674–3753` | Image-tagging plan (selection bar) | covered | — | Auto-tag selected with Apply automatically runs a job with the chosen model, thresholds and suggestion count (workspace-tagging-bulk.spec.mjs) |
+| Gallery thumbnail generation | `gallery.js:1852,1967` | S5/S7 | covered | `sources` · button · "Review options" · in "Thumbnail generation" | Start closes the dialog, toasts, and opens the job in Activity (workspace-system-sources.spec.mjs) |
+| Clear server thumbnails | `gallery.js:2175–2192` | S7 Maintenance | covered | `maintenance` · button · "Review options" · in "Thumbnail cache" | Thumbnail cache opens the S5 dialog (workspace-system-maintenance.spec.mjs) |
+| Browser cache clear | `gallery.js:2194–2207` | S7 Maintenance | covered | `maintenance` · button · "Review plan" · in "Metadata cache" | Metadata cache reviews and clears only owned browser entries when there are some (D102) (workspace-system-maintenance.spec.mjs) |
+| Refresh file listing | `gallery.js:2209` | S4 Sources | covered | `sources` · button · "Refresh" · in "Refresh files" | Refresh files calls /gallery/rescan and toasts its counts (workspace-system-sources.spec.mjs) |
+| Duplicate image scan, review, delete | `gallery.js:2234–2577` | S6/S7 Maintenance | covered | `maintenance` · button · "Find duplicates" | Find duplicates starts a job; its view links Review groups; Keep radios build a duplicate_files plan (D101) (workspace-system-maintenance.spec.mjs) |
+| Default view mode, image quality | `gallery-settings.js:26–27` | S3 Appearance | covered | `appearance` · combobox · "Default layout" | defaults apply to a new visit but not to the current view or a saved view (workspace-system.spec.mjs) |
+| Auto-load metadata, cache metadata, show file paths | `gallery-settings.js:31–33` | S3 Appearance | covered | `appearance` · switch · "Load metadata on selection" | metadata off shows an explicit load and loads once on request (workspace-system.spec.mjs) |
+| Video autoplay, mute, loop | `gallery-settings.js:40–42` | S3 Appearance | covered | `appearance` · switch · "Autoplay videos" | video defaults reach the viewer (workspace-system.spec.mjs) |
+| Image info on cards; sidebar collapsed | `gallery-settings.js:30,34` | S3 Appearance | covered | `appearance` · switch · "Show image details on cards" | added rows reach their consumers (workspace-system.spec.mjs) |
+| Reset gallery settings | `gallery.js:1813` | S3 Appearance | covered | `appearance` · button · "Reset" | reset restores defaults without touching other keys (workspace-system.spec.mjs) |
+| Lazy loading | `gallery-settings.js:25` | Legacy gallery (native always lazy) | kept in legacy | — | a legacy gallery Save keeps the workspace keys and every other stored key (gallery-settings.test.js) |
+| Results per page / grid columns / paged mode | `gallery-settings.js:28–29,35` | README continuous browsing | approved removal | — | numeric strings from <select> values are accepted and columns are clamped (gallery-settings.test.js) |
+| Startup thumbnail prompt | `gallery-settings.js:38–39`; `gallery.js:2578` | README; Overview thumbnail row | approved removal | — | thumbnail row reflects the status endpoint (workspace-system.spec.mjs) |
+| Client debug output `debugMode` | `gallery-settings.js:36` | Legacy gallery (S12-10) | kept in legacy | — | a legacy gallery Save keeps the workspace keys and every other stored key (gallery-settings.test.js) |
+| API timeout `apiTimeout` | `gallery-settings.js:37` | Legacy gallery (S12-10; read by no request) | kept in legacy | — | defaults are a complete, sane settings object (gallery-settings.test.js) |
+| config.json-only keys | `py/config.py:212–234,722–739`; `py/api/diagnostics_report.py:185` | S12 report (read-only) | covered | `diagnostics` · button · "Download diagnostic report" | test_report_lists_config_only_keys (test_api_diagnostics_report.py) |
+
 ### Browser cache ownership (#222)
 
 The legacy gallery's Clear cache used to delete every localStorage key starting `pm_` or
diff --git a/tests/browser/concept-inventory.mjs b/tests/browser/concept-inventory.mjs
index 4afd585..d04d2fd 100644
--- a/tests/browser/concept-inventory.mjs
+++ b/tests/browser/concept-inventory.mjs
@@ -676,3 +676,73 @@ export function measureInspector(selector) {
             primary:node.classList.contains('ca-primary'),minHeight:getComputedStyle(node).minHeight})),
     };
 }
+
+// #249 System S7 Task 20, shared since S12 (#329): the maintenance plan dialog's measurement and its D100 mapping,
+// moved unchanged from system-maintenance-concept.spec.mjs so the rotated-log review uses the same ones.
+/** Runs in the page: the open review dialog (plan or duplicates): its title, body and the concept's tokens. */
+export function measureReview() {
+    const dialog = document.querySelector('dialog#modal[open]');
+    const css = (node, ...keys) => node ? Object.fromEntries(keys.map(key => [key, getComputedStyle(node)[key]])) : null;
+    const name = node => [node.localName, ...[...node.classList].sort()].join('.');
+    const text = node => node?.textContent.trim() ?? null;
+    const body = dialog.querySelector('#modal-body');
+    const grid = body.querySelector(':scope > dl.meta-grid');
+    const compare = body.querySelector('.compare-grid');
+    const item = compare?.querySelector('.compare-item');
+    const notes = [...body.querySelectorAll(':scope > p.small')];
+    const note = notes.at(-1);
+    const actions = body.querySelector(':scope > .dialog-actions');
+    return {
+        title: text(dialog.querySelector('#modal-title')),
+        tree: [...body.children].map(name),
+        heading: body.querySelector(':scope > h3') && { text: text(body.querySelector(':scope > h3')),
+            ...css(body.querySelector(':scope > h3'), 'fontSize', 'fontWeight', 'color', 'marginBottom') },
+        grid: grid && { rows: [...grid.children].map(row => [text(row.querySelector('dt')), text(row.querySelector('dd'))]),
+            ...css(grid, 'display', 'gridTemplateColumns', 'columnGap', 'rowGap'),
+            dt: css(grid.querySelector('dt'), 'fontSize', 'color', 'textTransform'), dd: css(grid.querySelector('dd'), 'fontSize', 'color') },
+        details: body.querySelector(':scope > details') && { summary: text(body.querySelector(':scope > details > summary')),
+            tree: [...body.querySelector(':scope > details').children].map(name) },
+        backup: body.querySelector(':scope > .notice') && { tree: [...body.querySelector(':scope > .notice').children].map(name),
+            text: [...body.querySelectorAll(':scope > .notice > div:first-child > *')].map(node => [node.localName, text(node)]),
+            buttons: [...body.querySelectorAll(':scope > .notice button')].map(text) },
+        compare: compare && { tree: [...compare.children].map(name), ...css(compare, 'display', 'gridTemplateColumns', 'columnGap'),
+            items: [...compare.children].map(entry => ({ tree: [...entry.children].map(name), label: text(entry.querySelector('label')),
+                checked: entry.querySelector('input[type=radio]').checked, image: entry.querySelector('img')?.className ?? null })),
+            item: css(item, 'paddingTop', 'paddingLeft', 'backgroundColor', 'borderTopWidth', 'borderTopColor', 'borderTopLeftRadius'),
+            image: css(item.querySelector('img'), 'width', 'objectFit'),
+            label: css(item.querySelector('label'), 'fontSize', 'color'),
+            radio: { name: item.querySelector('input[type=radio]').name.startsWith('keep-') ? 'keep-*' : 'other',
+                type: item.querySelector('input').type } },
+        note: note && { text: text(note), ...css(note, 'fontSize', 'color', 'marginTop') },
+        actions: { tree: [...actions.children].map(name), ...css(actions, 'display', 'justifyContent', 'columnGap', 'marginTop'),
+            buttons: [...actions.children].map(item => ({ text: text(item), className: item.className,
+                ...css(item, 'backgroundColor', 'color', 'fontSize', 'paddingTop', 'paddingLeft', 'borderTopColor') })) },
+    };
+}
+
+export const BACKUP_BOX = Object.freeze({ tree: ['div', 'div.row-actions'], text: [['h3', 'Back up the database first (recommended)'],
+    ['p', 'Downloads a copy of the prompts database before this operation changes any records.']], buttons: ['Back up now'] });
+
+/**
+ * D100: the server's plan in the concept's dialog: the operation's row title as its `h3` (the concept prints its
+ * `data-plan` name), the four rows with the plan's values, the listed records (`details`), the hold line in the
+ * concept's `p.small`, the D55 backup box before the actions, and "Apply reviewed operation". No sample note.
+ */
+export function mapPlanConcept(reference, title, plan) {
+    const backup = plan.backup.policy === 'off' ? 'No safety backup (the policy is off)'
+        : `Create and verify before changes (${plan.backup.destination_label})`;
+    const tree = ['h3', 'dl.meta-grid', ...(plan.details.length ? ['details'] : []), 'p.small', 'div.notice', 'div.dialog-actions'];
+    const [cancel, apply] = reference.actions.buttons;
+    return {
+        ...reference,
+        tree,
+        heading: { ...reference.heading, text: title },
+        grid: { ...reference.grid, rows: [['Scope', plan.scope.label],
+            ['Protected', plan.protected.reasons.length ? plan.protected.reasons.join(' · ') : 'Nothing is protected'],
+            ['Backup', backup], ['Media on disk', plan.media.label]] },
+        details: plan.details.length ? { summary: `Listed records (${plan.details.length})`, tree: ['summary', 'pre'] } : null,
+        backup: BACKUP_BOX,
+        note: { ...reference.note, text: 'Nothing changes until you apply. This review holds for 15 minutes.' },
+        actions: { ...reference.actions, buttons: [cancel, { ...apply, text: 'Apply reviewed operation' }] },
+    };
+}
diff --git a/tests/browser/system-diagnostics-concept.spec.mjs b/tests/browser/system-diagnostics-concept.spec.mjs
new file mode 100644
index 0000000..af459cd
--- /dev/null
+++ b/tests/browser/system-diagnostics-concept.spec.mjs
@@ -0,0 +1,396 @@
+import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
+import { test, expect } from './fixtures.mjs';
+import { SIZES, THEMES, seedConcept, openConcept, openProduction, diffInventory, mutate, measureReview, mapPlanConcept }
+    from './concept-inventory.mjs';
+
+// #249 System S12 Task 7 (#329): System › Diagnostics & logs (app.js renderSystem 694–695) and its log cleanup review
+// (the concept's `maintenancePlan("rotated logs")`, 953–958) against the immutable concept, on the concept-shaped
+// fixture with the logger writing into this server's own root and seeded with the concept's sample (four lines, a
+// 1.4 MB active log, three rotated copies, console logging off). Each concept measurement is mapped only by the recorded
+// deviations (D109, D110, and D100 for the review), each commented where it applies; after that the difference must be
+// empty, and a removed term, a renamed button, a reordered option, a primary Refresh, a squeezed select or a swapped
+// token must be noticed.
+test.use({ locale: 'en-US', timezoneId: 'UTC' });
+
+test.beforeEach(async ({ page, request, browserName }) => {
+    await startCoverage(page, browserName);
+    await seedConcept(request);
+    await expect(await request.post('/__test__/system/reset')).toBeOK();
+    await expect(await request.post('/__test__/jobs/restart')).toBeOK();
+    await expect(await request.post('/__test__/logs/reset')).toBeOK();
+    await expect(await request.post('/__test__/logs/seed', { data: { mode: 'concept' } })).toBeOK();
+    page.conceptErrors = [];
+    page.on('pageerror', error => page.conceptErrors.push(error.message));
+});
+
+test.afterEach(async ({ page, request, browserName }) => {
+    await saveCoverage(page, browserName);
+    await request.post('/__test__/jobs/restart');
+    await request.post('/__test__/logs/reset');
+    await request.post('/__test__/system/reset');
+    expect(page.conceptErrors).toEqual([]);
+});
+
+const REPORT_URL = '/prompt_manager/system/diagnostics';
+const PREVIEW_URL = '/prompt_manager/maintenance/preview';
+const LINE_FORMAT = /^\d\d:\d\d:\d\d [A-Z]+ +\S/;
+
+/** Runs in the page: Diagnostics & logs under `mainSelector`: every surface's text, controls, geometry and tokens. */
+function measureDiagnostics([mainSelector, lineFormat]) {
+    const format = new RegExp(lineFormat);
+    const layout = document.querySelector(`${mainSelector} .settings-layout`);
+    const css = (node, ...keys) => node ? Object.fromEntries(keys.map(key => [key, getComputedStyle(node)[key]])) : null;
+    const tokens = (node, ...names) => Object.fromEntries(names.map(key => [key, getComputedStyle(node).getPropertyValue(key).trim()]));
+    const name = node => [node.localName, ...[...node.classList].sort()].join('.');
+    const text = node => node?.textContent.trim() ?? null;
+    const button = node => ({ text: text(node), className: node.className });
+    const control = row => {
+        const select = row.querySelector(':scope > select');
+        if (select) return { kind: 'select', id: select.id, options: [...select.options].map(option => option.textContent),
+            selected: select.selectedOptions[0]?.textContent ?? null, disabled: select.disabled };
+        const toggle = row.querySelector(':scope > * input[type="checkbox"]');
+        return toggle ? { kind: 'switch', id: toggle.id, wrapper: name(toggle.parentElement), checked: toggle.checked,
+            disabled: toggle.disabled } : null;
+    };
+    const operations = parent => [...parent.querySelectorAll(':scope > .operation')].map(row => ({ tree: [...row.children].map(name),
+        title: text(row.querySelector('h3')), description: text(row.querySelector('p')),
+        actions: [...row.querySelectorAll('.row-actions > button')].map(button) }));
+    const toolbarItem = node => ({ name: name(node), text: node.localName === 'select' || node.localName === 'input' ? null : text(node),
+        for: node.localName === 'label' ? node.htmlFor : null, id: node.id || null,
+        options: node.localName === 'select' ? [...node.options].map(option => option.textContent) : null,
+        // The chosen option, so a wrong default level is noticed.
+        selected: node.localName === 'select' ? node.selectedOptions[0]?.textContent ?? null : null,
+        input: node.localName === 'input' ? [node.type, node.min, node.max, node.value] : null,
+        className: node.localName === 'button' ? node.className : null });
+    const surfaces = [...layout.querySelectorAll(':scope > section.surface')];
+    const pre = layout.querySelector('pre');
+    const lines = (pre?.textContent ?? '').split('\n').filter(Boolean);
+    const details = layout.querySelector('details');
+    const firstRow = layout.querySelector('.setting-row');
+    const toolbar = layout.querySelector('.toolbar');
+    return {
+        layout: [...layout.children].map(name),
+        surfaces: surfaces.map(surface => {
+            const heading = surface.querySelector(':scope > .panel-heading');
+            const grid = surface.querySelector(':scope > .meta-grid');
+            return {
+                tree: [...surface.children].map(name),
+                heading: text(surface.querySelector(':scope > h2, :scope > .panel-heading > h2')),
+                panelHeading: heading && [...heading.children].map(node => [name(node), text(node)]),
+                grid: grid && [...grid.children].map(entry => [name(entry), text(entry.querySelector('dt')), text(entry.querySelector('dd'))]),
+                buttons: [...surface.querySelectorAll(':scope > button')].map(button),
+                toolbar: surface.querySelector(':scope > .toolbar') && [...surface.querySelector(':scope > .toolbar').children].map(toolbarItem),
+                pre: surface.querySelector(':scope > pre') && { tabIndex: pre.tabIndex, tree: [...pre.children].map(name), lines,
+                    format: lines.every(line => format.test(line)) },
+                notes: [...surface.querySelectorAll(':scope > p')].map(node => [name(node), text(node), node.getAttribute('role'),
+                    node.getAttribute('aria-label')]),
+                rows: [...surface.querySelectorAll(':scope > .setting-row')].map(row => ({ tree: [...row.children].map(name),
+                    text: [...row.firstElementChild.children].map(node => [name(node), text(node), node.localName === 'label' ? node.htmlFor : null]),
+                    control: control(row) })),
+                details: surface.querySelector(':scope > details') && {
+                    summary: text(details.querySelector(':scope > summary')), tree: [...details.children].map(name),
+                    notes: [...details.querySelectorAll(':scope > p')].map(node => [name(node), text(node)]),
+                    buttons: [...details.querySelectorAll(':scope > button')].map(button),
+                    files: [...details.querySelectorAll(':scope > .operation-list > .operation')].map(row => ({
+                        title: text(row.querySelector('h3')), detail: text(row.querySelector('p')), actions: [...row.querySelectorAll('.row-actions > button')].map(item =>
+                            [text(item), item.getAttribute('aria-label')]) })),
+                    operations: operations(details) },
+                operations: operations(surface),
+            };
+        }),
+        tokens: tokens(surfaces[0], '--line', '--panel', '--accent'),
+        surface: css(surfaces[1], 'paddingTop', 'paddingLeft', 'backgroundColor', 'borderTopWidth', 'borderTopColor', 'borderTopLeftRadius',
+            'marginTop'),
+        grid: css(layout.querySelector('.meta-grid'), 'display', 'gridTemplateColumns', 'columnGap', 'rowGap'),
+        toolbar: css(toolbar, 'display', 'flexWrap', 'alignItems', 'columnGap', 'rowGap', 'marginBottom'),
+        pre: css(pre, 'fontFamily', 'fontSize', 'backgroundColor', 'borderTopColor', 'borderTopLeftRadius', 'paddingTop', 'overflowX'),
+        row: css(firstRow, 'display', 'alignItems', 'justifyContent', 'columnGap', 'paddingTop', 'paddingBottom', 'borderTopWidth',
+            'borderTopColor'),
+        label: css(firstRow.querySelector('label'), 'fontSize', 'fontWeight', 'color'),
+        description: css(firstRow.querySelector('p'), 'fontSize', 'color', 'marginTop'),
+        select: css(firstRow.querySelector('select'), 'fontSize', 'minWidth', 'maxWidth', 'backgroundColor', 'color', 'borderTopColor'),
+        summary: css(details.querySelector('summary'), 'fontSize', 'fontWeight', 'color', 'cursor'),
+        small: css(details.querySelector(':scope > p.small'), 'fontSize', 'color'),
+        // Whether each select is as wide as the browser lays out a copy holding only its chosen option, i.e. it shows
+        // that option whole (the browser's own select sizing, arrow included).
+        selectsFit: [...layout.querySelectorAll('select')].map(select => {
+            const copy = select.cloneNode(false);
+            copy.removeAttribute('id');
+            copy.append(new Option(select.selectedOptions[0]?.textContent ?? ''));
+            Object.assign(copy.style, { position: 'absolute', visibility: 'hidden', width: 'max-content', minWidth: '0',
+                maxWidth: 'none', flex: 'none' });
+            select.parentElement.append(copy);
+            const needed = copy.getBoundingClientRect().width;
+            copy.remove();
+            return select.getBoundingClientRect().width + 0.5 >= needed;
+        }),
+        pageScroll: document.documentElement.scrollWidth > document.documentElement.clientWidth,
+    };
+}
+
+const plural = (count, one, many = `${one}s`) => `${count.toLocaleString('en-US')} ${count === 1 ? one : many}`;
+/** The server's size label (1 KB = 1024 bytes), as the section prints it. */
+function sizeText(bytes) {
+    if (bytes < 1024) return plural(bytes, 'byte');
+    if (bytes < 2 ** 20) return `${(bytes / 2 ** 10).toFixed(1)} KB`;
+    if (bytes < 2 ** 30) return `${(bytes / 2 ** 20).toFixed(1)} MB`;
+    return `${(bytes / 2 ** 30).toFixed(1)} GB`;
+}
+
+const KINDS = Object.freeze({ active: 'Active log', rotated: 'Rotated copy', other: 'Other file' });
+const RENDERER_NONE = 'No ComfyUI window is open in this browser, so its renderer is not known.';
+const COPY = Object.freeze({
+    testLink: 'Write a placeholder image record to check that linking works.',
+    runtimeLevel: 'How much the server writes to the log. Applied until the server restarts.',
+    console: 'Print Prompt Manager’s warnings and errors in the ComfyUI console (everything at DEBUG). Applied until the server restarts.',
+    clear: 'Empty the active log and delete its rotated copies.',
+    retention: 'Rotates at 10 MB · keeps 5 rotated copies · file logging on · memory buffer 1,000 entries',
+});
+
+/**
+ * The concept's Diagnostics & logs with the recorded deviations applied, for the server's `report` and the seeded
+ * `files` (`/logs/files`). The concept's own sample values the fixture reproduces stay as they are: the four log lines,
+ * the Viewer.js line, "prompt_manager.log · 1.4 MB · rotated copies: 3", INFO and console logging off.
+ */
+function mapDiagnosticsConcept(reference, { report, files, stats }) {
+    const [diagnostics, logs] = reference.surfaces;
+    const [levelLabel, level, refresh, download] = logs.toolbar;
+    const [runtime, consoleRow] = logs.rows;
+    const database = report.checks.database;
+    const { configured, watching, unavailable } = report.sources;
+    const sources = configured === 0 ? `ComfyUI output folder · ${watching ? 'watching' : 'manual scan'}`
+        : unavailable > 0 ? `${plural(configured, 'source')} · ${unavailable} not available`
+            : `${plural(configured, 'source')} · ${watching} watching`;
+    const errors = (stats.level_counts.ERROR ?? 0) + (stats.level_counts.CRITICAL ?? 0);
+    return {
+        ...reference,
+        surfaces: [
+            { ...diagnostics,
+                // D110: the Test image link operation follows the concept's Image-link diagnostics.
+                tree: [...diagnostics.tree, 'div.operation'],
+                // D110: live values. Database and Sources from `GET /system/diagnostics`, Host renderers is D106's
+                // renderer line (no ComfyUI window in this browser); the pinned Viewer.js line is the concept's own.
+                grid: diagnostics.grid.map(([entry, term, value]) => [entry, term, {
+                    Database: `Readable · ${sizeText(report.database_info.database_size_bytes)} · ${plural(database.image_count, 'image')}`,
+                    Sources: sources,
+                    'Host renderers': RENDERER_NONE }[term] ?? value]),
+                // D110: the buttons drop the concept's "sample".
+                buttons: diagnostics.buttons.map(item => ({ ...item, text: item.text.replace('Download sample diagnostic report',
+                    'Download diagnostic report') })),
+                operations: [
+                    // D110: "Inspect" opens the read-only Inspect a file page.
+                    ...diagnostics.operations.map(row => ({ ...row, actions: row.actions.map(item => ({ ...item, text: 'Inspect' })) })),
+                    // D110: the legacy synthetic link (S12-11), enabled: the fixture has a most recent prompt.
+                    { ...diagnostics.operations[0], title: 'Test image link', description: COPY.testLink,
+                        actions: [{ ...diagnostics.operations[0].actions[0], text: 'Create test link…' }] },
+                ] },
+            { ...logs,
+                // D109: the statistics line follows the viewer.
+                tree: [logs.tree[0], logs.tree[1], logs.tree[2], 'p.small', ...logs.tree.slice(3)],
+                toolbar: [
+                    levelLabel,
+                    // D109: all six minimum levels (the concept has three).
+                    { ...level, options: ['All levels', 'DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL'] },
+                    // D109: the added Lines control, 1–500, default 100.
+                    { name: 'label.small', text: 'Lines', for: 'log-limit', id: null, options: null, selected: null, input: null,
+                        className: null },
+                    { name: 'input', text: null, for: null, id: 'log-limit', options: null, selected: null,
+                        input: ['number', '1', '500', '100'], className: null },
+                    refresh,
+                    // D109: the active log, not a sample.
+                    { ...download, text: 'Download log' },
+                ],
+                // D109: "Log statistics" (errors are ERROR + CRITICAL).
+                notes: [['p.small', `${plural(stats.buffer_count, 'entry', 'entries')} in memory · ${plural(errors, 'error')} · `
+                    + `${plural(stats.level_counts.WARNING ?? 0, 'warning')} · ${plural(stats.log_files_count, 'file')} · `
+                    + `${sizeText(stats.total_log_size)} on disk`, 'status', 'Log statistics']],
+                rows: [
+                    // D109: CRITICAL after the concept's levels; the value lasts until the server restarts.
+                    { ...runtime, text: [runtime.text[0], ['p', COPY.runtimeLevel, null]],
+                        control: { ...runtime.control, options: [...runtime.control.options, 'CRITICAL'] } },
+                    // D109: what the console setting does and that it lasts until the server restarts (off, as the
+                    // concept's sample, by the fixture's seed).
+                    { ...consoleRow, text: [consoleRow.text[0], ['p', COPY.console, null]] },
+                ],
+                details: { ...logs.details,
+                    // D109: the retention line, the files and Clear all logs follow the concept's line and review.
+                    tree: [...logs.details.tree, 'p.small', 'div.operation-list', 'div.operation'],
+                    notes: [...logs.details.notes, ['p.small', COPY.retention]],
+                    files: files.map(row => ({ title: row.filename, detail: `${sizeText(row.size)} · ${row.modified.slice(0, 16)
+                        .replace('T', ' ')} · ${KINDS[row.kind]}`, actions: [['Download', `Download ${row.filename}`]] })),
+                    operations: [{ tree: ['div', 'div.row-actions'], title: 'Clear all logs', description: COPY.clear,
+                        actions: [{ text: 'Clear all logs…', className: 'danger' }] }] } },
+        ],
+    };
+}
+
+async function conceptDiagnostics(page, theme) {
+    await openConcept(page, 'system', theme);
+    await page.locator('#main .section-nav').getByRole('button', { name: 'Diagnostics & logs', exact: true }).click();
+    await expect(page.locator('#main .settings-layout > section.surface')).toHaveCount(2);
+    await page.mouse.move(0, 0);
+    return page.evaluate(measureDiagnostics, ['#main', LINE_FORMAT.source]);
+}
+
+/** Production's section once every read answered, with the server's report, files and statistics it shows. */
+async function productionDiagnostics(page, request, theme) {
+    await openProduction(page, 'system/diagnostics', theme);
+    const main = page.locator('#workspace-main');
+    await expect(main.locator('.settings-layout > section.surface')).toHaveCount(2);
+    await expect(main.locator('.meta-grid dd')).not.toContainText(['Loading…']);
+    await expect(main.locator('.meta-grid dd').last()).toHaveText(RENDERER_NONE);
+    await expect(main.locator('#log-lines')).not.toHaveText('Loading…');
+    await expect(main.locator('#log-stats')).not.toHaveText('Loading…');
+    await expect(main.locator('details > p.small')).not.toContainText(['Loading…']);
+    await expect(main.locator('#runtime-level')).toBeEnabled();
+    await expect(main.locator('.operation').filter({ hasText: 'Create test link…' }).locator('button')).not.toHaveAttribute('aria-disabled', 'true');
+    await page.mouse.move(0, 0);
+    const production = await page.evaluate(measureDiagnostics, ['#workspace-main', LINE_FORMAT.source]);
+    const read = async url => (await request.get(url)).json();
+    const report = await read(REPORT_URL);
+    const { files } = await read('/prompt_manager/logs/files');
+    const { stats } = await read('/prompt_manager/logs/stats');
+    return { production, report, files, stats };
+}
+
+for (const theme of THEMES) for (const [width, height] of SIZES) {
+    test(`diagnostics and logs match the concept ${theme} ${width}x${height}`, async ({ page, request }, testInfo) => {
+        await page.setViewportSize({ width, height });
+        const concept = await conceptDiagnostics(page, theme);
+        await page.screenshot({ path: testInfo.outputPath(`concept-diagnostics-${theme}-${width}.png`), fullPage: true });
+        const { production, ...live } = await productionDiagnostics(page, request, theme);
+        await page.screenshot({ path: testInfo.outputPath(`production-diagnostics-${theme}-${width}.png`), fullPage: true });
+        expect(diffInventory(mapDiagnosticsConcept(concept, live), production)).toEqual([]);
+        expect(production.surfaces[1].pre.format).toBe(true);
+        expect(production.pageScroll).toBe(false);
+    });
+}
+
+// Below the concept's smallest size: on a 320px phone the Level and Runtime log level selects still show their whole
+// option, without page scroll.
+for (const theme of THEMES) test(`diagnostics selects fit at 320 wide ${theme}`, async ({ page, request }) => {
+    await page.setViewportSize({ width: 320, height: 700 });
+    const { production } = await productionDiagnostics(page, request, theme);
+    expect(production.selectsFit).toEqual([true, true]);
+    expect(production.pageScroll).toBe(false);
+});
+
+/**
+ * D100 with D109's rule for this plan: the server's `rotated_logs` plan in the concept's dialog, "Rotated log copies"
+ * as its `h3`, the plan's grid values (its Backup row says none is needed), "Listed files (N)", the hold line, no D55
+ * backup box (nothing in the library changes) and "Apply reviewed operation".
+ */
+function mapCleanupConcept(reference, plan) {
+    const mapped = mapPlanConcept(reference, 'Rotated log copies', plan);
+    return {
+        ...mapped,
+        // D109: no backup box for a plan that changes no library record.
+        tree: mapped.tree.filter(item => item !== 'div.notice'),
+        grid: { ...mapped.grid, rows: mapped.grid.rows.map(([term, value]) =>
+            [term, term === 'Backup' ? 'Not needed: no library record changes' : value]) },
+        backup: null,
+        // D109: the plan lists files, not records.
+        details: { ...mapped.details, summary: `Listed files (${plan.details.length})` },
+    };
+}
+
+async function conceptCleanup(page, theme) {
+    await conceptDiagnostics(page, theme);
+    await page.locator('#main details > summary').click();
+    await page.locator('#main [data-plan="rotated logs"]').click();
+    await expect(page.locator('dialog#modal[open] #modal-title')).toHaveText('Review maintenance plan');
+    await page.mouse.move(0, 0);
+    return page.evaluate(measureReview);
+}
+
+async function productionCleanup(page, request, theme) {
+    await productionDiagnostics(page, request, theme);
+    await page.locator('#workspace-main details > summary').click();
+    const answer = page.waitForResponse(response => response.url().endsWith(PREVIEW_URL));
+    await page.locator('#workspace-main').getByRole('button', { name: 'Review log cleanup', exact: true }).click();
+    const plan = await (await answer).json();
+    await expect(page.locator('dialog#modal[open] #modal-body > h3')).toHaveText('Rotated log copies');
+    await page.mouse.move(0, 0);
+    return { plan, production: await page.evaluate(measureReview) };
+}
+
+for (const theme of THEMES) for (const [width, height] of SIZES) {
+    test(`log cleanup review matches the concept ${theme} ${width}x${height}`, async ({ page, request }, testInfo) => {
+        await page.setViewportSize({ width, height });
+        const concept = await conceptCleanup(page, theme);
+        expect(concept.heading.text).toBe('rotated logs');
+        expect(concept.tree).toEqual(['p.demo-note', 'h3', 'dl.meta-grid', 'p.small', 'div.dialog-actions']);
+        await page.screenshot({ path: testInfo.outputPath(`concept-log-cleanup-${theme}-${width}.png`) });
+        const { plan, production } = await productionCleanup(page, request, theme);
+        expect(plan.operation).toBe('rotated_logs');
+        await page.screenshot({ path: testInfo.outputPath(`production-log-cleanup-${theme}-${width}.png`) });
+        expect(diffInventory(mapCleanupConcept(concept, plan), production)).toEqual([]);
+    });
+}
+
+// Every path where production differs from the unmapped concept: D110's live values (Viewer.js is the concept's own),
+// renamed buttons and added operation, and D109's toolbar, statistics line, runtime rows and log files.
+const DEVIATED_PATHS = [
+    'surfaces.0.buttons.0', 'surfaces.0.grid.0', 'surfaces.0.grid.1', 'surfaces.0.grid.3', 'surfaces.0.operations.0',
+    'surfaces.0.operations.1', 'surfaces.0.operations.length', 'surfaces.0.tree.4', 'surfaces.0.tree.length',
+    'surfaces.1.details.files', 'surfaces.1.details.notes', 'surfaces.1.details.operations', 'surfaces.1.details.tree',
+    'surfaces.1.notes.0', 'surfaces.1.notes.length', 'surfaces.1.rows.0', 'surfaces.1.rows.1', 'surfaces.1.toolbar.1',
+    'surfaces.1.toolbar.2', 'surfaces.1.toolbar.3', 'surfaces.1.toolbar.4', 'surfaces.1.toolbar.5', 'surfaces.1.toolbar.length',
+    'surfaces.1.tree.3', 'surfaces.1.tree.5', 'surfaces.1.tree.6', 'surfaces.1.tree.length'].sort();
+
+test('diagnostics comparison detects mutations', async ({ page, request }) => {
+    await page.setViewportSize({ width: 1600, height: 1100 });
+    const concept = await conceptDiagnostics(page, 'dark');
+    const { production, ...live } = await productionDiagnostics(page, request, 'dark');
+    const expected = mapDiagnosticsConcept(concept, live);
+    expect(diffInventory(expected, production)).toEqual([]);
+    // Unmapped, the section differs only where D109 and D110 are recorded.
+    expect(diffInventory(concept, production).map(item => item.path.split('.').slice(0, 4).join('.'))
+        .filter((path, index, all) => all.indexOf(path) === index).sort()).toEqual(DEVIATED_PATHS);
+    const measure = () => page.evaluate(measureDiagnostics, ['#workspace-main', LINE_FORMAT.source]);
+    const paths = async () => diffInventory(expected, await measure()).map(item => item.path);
+    // A removed term.
+    const undoTerm = await mutate(page, { remove: ['#workspace-main .meta-grid > div:nth-child(2)'] });
+    expect(await paths()).toEqual(expect.arrayContaining(['surfaces.0.grid.length']));
+    await undoTerm();
+    // A renamed button.
+    await page.evaluate(() => { document.querySelector('#workspace-main section.surface > button').textContent = 'Download report'; });
+    expect(await paths()).toEqual(['surfaces.0.buttons.0.text']);
+    await page.evaluate(() => { document.querySelector('#workspace-main section.surface > button').textContent = 'Download diagnostic report'; });
+    // A reordered level option.
+    await page.evaluate(() => { const select = document.querySelector('#workspace-main #log-level'); select.append(select.options[1]); });
+    expect(await paths()).toEqual(expect.arrayContaining(['surfaces.1.toolbar.1.options.1']));
+    await page.evaluate(() => { const select = document.querySelector('#workspace-main #log-level'); select.insertBefore(select.options[5], select.options[1]); });
+    // A wrong default level.
+    await page.evaluate(() => { document.querySelector('#workspace-main #log-level').value = 'INFO'; });
+    expect(await paths()).toEqual(['surfaces.1.toolbar.1.selected']);
+    await page.evaluate(() => { document.querySelector('#workspace-main #log-level').value = ''; });
+    // A primary Refresh.
+    await page.evaluate(() => { document.querySelectorAll('#workspace-main .toolbar > button')[0].classList.add('ca-primary'); });
+    expect(await paths()).toEqual(expect.arrayContaining(['surfaces.1.toolbar.4.className']));
+    await page.evaluate(() => { document.querySelectorAll('#workspace-main .toolbar > button')[0].classList.remove('ca-primary'); });
+    // A select squeezed until its chosen option is cut.
+    const undoSqueeze = await mutate(page, { css: '#workspace-main #runtime-level { max-width: 30px !important; min-width: 0 !important; }' });
+    expect(await paths()).toEqual(expect.arrayContaining(['selectsFit.1']));
+    await undoSqueeze();
+    // A swapped token.
+    const undoToken = await mutate(page, { css: '#workspace-main .settings-layout { --line: rgb(255, 0, 0); }' });
+    expect(await paths()).toEqual(expect.arrayContaining(['tokens.--line', 'row.borderTopColor']));
+    await undoToken();
+    expect(diffInventory(expected, await measure())).toEqual([]);
+
+    // The log cleanup review: a changed grid term, a backup box that came back and a grid token are noticed.
+    const conceptReview = await conceptCleanup(page, 'dark');
+    const { plan } = await productionCleanup(page, request, 'dark');
+    const expectedReview = mapCleanupConcept(conceptReview, plan);
+    const reviewPaths = async () => diffInventory(expectedReview, await page.evaluate(measureReview)).map(item => item.path);
+    expect(await reviewPaths()).toEqual([]);
+    await page.evaluate(() => { document.querySelectorAll('dialog#modal[open] dl.meta-grid dt')[2].textContent = 'Safety'; });
+    expect(await reviewPaths()).toEqual(['grid.rows.2.0']);
+    await page.evaluate(() => { document.querySelectorAll('dialog#modal[open] dl.meta-grid dt')[2].textContent = 'Backup'; });
+    const undoGrid = await mutate(page, { css: 'dialog#modal dl.meta-grid { column-gap: 3px; }' });
+    expect(await reviewPaths()).toEqual(expect.arrayContaining(['grid.columnGap']));
+    await undoGrid();
+    expect(await reviewPaths()).toEqual([]);
+});
+
diff --git a/tests/browser/system-maintenance-concept.spec.mjs b/tests/browser/system-maintenance-concept.spec.mjs
index 89812cd..cf2007d 100644
--- a/tests/browser/system-maintenance-concept.spec.mjs
+++ b/tests/browser/system-maintenance-concept.spec.mjs
@@ -1,6 +1,7 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
 import { test, expect } from './fixtures.mjs';
-import { SIZES, THEMES, seedConcept, openConcept, openProduction, diffInventory, mutate } from './concept-inventory.mjs';
+import { SIZES, THEMES, seedConcept, openConcept, openProduction, diffInventory, mutate, measureReview, mapPlanConcept }
+    from './concept-inventory.mjs';
 
 // #249 System S7 Task 20: System › Maintenance (app.js renderSystem 688–690), its plan dialog (`maintenancePlan`,
 // 953–958) for each operation and its duplicates dialog (`duplicates`, 1457–1461) against the immutable concept, on
@@ -103,47 +104,6 @@ for (const theme of THEMES) for (const [width, height] of SIZES) {
     });
 }
 
-/** Runs in the page: the open review dialog (plan or duplicates): its title, body and the concept's tokens. */
-function measureReview() {
-    const dialog = document.querySelector('dialog#modal[open]');
-    const css = (node, ...keys) => node ? Object.fromEntries(keys.map(key => [key, getComputedStyle(node)[key]])) : null;
-    const name = node => [node.localName, ...[...node.classList].sort()].join('.');
-    const text = node => node?.textContent.trim() ?? null;
-    const body = dialog.querySelector('#modal-body');
-    const grid = body.querySelector(':scope > dl.meta-grid');
-    const compare = body.querySelector('.compare-grid');
-    const item = compare?.querySelector('.compare-item');
-    const notes = [...body.querySelectorAll(':scope > p.small')];
-    const note = notes.at(-1);
-    const actions = body.querySelector(':scope > .dialog-actions');
-    return {
-        title: text(dialog.querySelector('#modal-title')),
-        tree: [...body.children].map(name),
-        heading: body.querySelector(':scope > h3') && { text: text(body.querySelector(':scope > h3')),
-            ...css(body.querySelector(':scope > h3'), 'fontSize', 'fontWeight', 'color', 'marginBottom') },
-        grid: grid && { rows: [...grid.children].map(row => [text(row.querySelector('dt')), text(row.querySelector('dd'))]),
-            ...css(grid, 'display', 'gridTemplateColumns', 'columnGap', 'rowGap'),
-            dt: css(grid.querySelector('dt'), 'fontSize', 'color', 'textTransform'), dd: css(grid.querySelector('dd'), 'fontSize', 'color') },
-        details: body.querySelector(':scope > details') && { summary: text(body.querySelector(':scope > details > summary')),
-            tree: [...body.querySelector(':scope > details').children].map(name) },
-        backup: body.querySelector(':scope > .notice') && { tree: [...body.querySelector(':scope > .notice').children].map(name),
-            text: [...body.querySelectorAll(':scope > .notice > div:first-child > *')].map(node => [node.localName, text(node)]),
-            buttons: [...body.querySelectorAll(':scope > .notice button')].map(text) },
-        compare: compare && { tree: [...compare.children].map(name), ...css(compare, 'display', 'gridTemplateColumns', 'columnGap'),
-            items: [...compare.children].map(entry => ({ tree: [...entry.children].map(name), label: text(entry.querySelector('label')),
-                checked: entry.querySelector('input[type=radio]').checked, image: entry.querySelector('img')?.className ?? null })),
-            item: css(item, 'paddingTop', 'paddingLeft', 'backgroundColor', 'borderTopWidth', 'borderTopColor', 'borderTopLeftRadius'),
-            image: css(item.querySelector('img'), 'width', 'objectFit'),
-            label: css(item.querySelector('label'), 'fontSize', 'color'),
-            radio: { name: item.querySelector('input[type=radio]').name.startsWith('keep-') ? 'keep-*' : 'other',
-                type: item.querySelector('input').type } },
-        note: note && { text: text(note), ...css(note, 'fontSize', 'color', 'marginTop') },
-        actions: { tree: [...actions.children].map(name), ...css(actions, 'display', 'justifyContent', 'columnGap', 'marginTop'),
-            buttons: [...actions.children].map(item => ({ text: text(item), className: item.className,
-                ...css(item, 'backgroundColor', 'color', 'fontSize', 'paddingTop', 'paddingLeft', 'borderTopColor') })) },
-    };
-}
-
 // The concept's plan names (`data-plan`) and production's operation, row and button for each.
 const PLANS = Object.freeze([
     ['duplicate prompts', 'duplicate_prompts', 'Duplicate prompt text'],
@@ -151,32 +111,6 @@ const PLANS = Object.freeze([
     ['unused prompt components', 'unused_components', 'Unused prompt components'],
     ['missing-file links', 'missing_links', 'Missing-file links'],
 ]);
-const BACKUP_BOX = Object.freeze({ tree: ['div', 'div.row-actions'], text: [['h3', 'Back up the database first (recommended)'],
-    ['p', 'Downloads a copy of the prompts database before this operation changes any records.']], buttons: ['Back up now'] });
-
-/**
- * D100: the server's plan in the concept's dialog: the operation's row title as its `h3` (the concept prints its
- * `data-plan` name), the four rows with the plan's values, the listed records (`details`), the hold line in the
- * concept's `p.small`, the D55 backup box before the actions, and "Apply reviewed operation". No sample note.
- */
-function mapPlanConcept(reference, title, plan) {
-    const backup = plan.backup.policy === 'off' ? 'No safety backup (the policy is off)'
-        : `Create and verify before changes (${plan.backup.destination_label})`;
-    const tree = ['h3', 'dl.meta-grid', ...(plan.details.length ? ['details'] : []), 'p.small', 'div.notice', 'div.dialog-actions'];
-    const [cancel, apply] = reference.actions.buttons;
-    return {
-        ...reference,
-        tree,
-        heading: { ...reference.heading, text: title },
-        grid: { ...reference.grid, rows: [['Scope', plan.scope.label],
-            ['Protected', plan.protected.reasons.length ? plan.protected.reasons.join(' · ') : 'Nothing is protected'],
-            ['Backup', backup], ['Media on disk', plan.media.label]] },
-        details: plan.details.length ? { summary: `Listed records (${plan.details.length})`, tree: ['summary', 'pre'] } : null,
-        backup: BACKUP_BOX,
-        note: { ...reference.note, text: 'Nothing changes until you apply. This review holds for 15 minutes.' },
-        actions: { ...reference.actions, buttons: [cancel, { ...apply, text: 'Apply reviewed operation' }] },
-    };
-}
 
 async function conceptPlan(page, theme, name) {
     await conceptMaintenance(page, theme);
diff --git a/tests/browser/workspace-system.spec.mjs b/tests/browser/workspace-system.spec.mjs
index 0988f99..7dab866 100644
--- a/tests/browser/workspace-system.spec.mjs
+++ b/tests/browser/workspace-system.spec.mjs
@@ -1,6 +1,7 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
 import { test, expect } from './fixtures.mjs';
 import { seedConcept } from './concept-inventory.mjs';
+import { readCoverageTable, parseControl, CONTROL_EXEMPTIONS } from '../../tools/vendor/legacy-coverage.mjs';
 
 // System › Overview (#249 System S2 Task 6) on the concept-shaped real fixture: the metrics, rows, Statistics dialog and
 // Health report read the server, never sample values (D93, D95, D96). The hooks are workspace_system_fixture.py's.
@@ -794,3 +795,45 @@ test('reset restores defaults without touching other keys', async ({ page }) =>
     expect(stored).toEqual({ gridColumns: 5, defaultLimit: 200, thumbnailPromptDismissed: 'kept', workspaceLayout: 'grid',
         videoMute: true, showImageInfo: true });
 });
+
+// TESTING.md "Legacy System capability coverage" (#249 System S12, #329): each `covered` row's native control is on its
+// System section, found by role and accessible name (a `term` by its text, a disclosure by its summary). Collapsed
+// `details` are opened first, so a control inside one counts once it is shown. tests/vendor/legacy-coverage.test.mjs
+// checks the rest of each row.
+test('every covered legacy System capability has its native control', async ({ page, request }) => {
+    // Download is offered for a model that is not on disk ("Download again" otherwise): the selected default's file is
+    // missing here.
+    await expect(await request.post('/__test__/tagging/models', { data: { unavailable: ['wd14-swinv2'] } })).toBeOK();
+    try {
+        await findControls(page);
+    } finally {
+        await request.post('/__test__/tagging/reset', { data: {} });
+    }
+});
+
+async function findControls(page) {
+    const covered = readCoverageTable().filter(row => row.Status === 'covered')
+        .map(row => ({ capability: row.Capability, ...parseControl(row['Native control']) }));
+    // A covered row without a control is one of the recorded exemptions, never silently skipped.
+    expect(covered.filter(row => !row.section).map(row => row.capability)).toEqual(Object.keys(CONTROL_EXEMPTIONS));
+    const controls = covered.filter(row => row.section);
+    expect(controls.length).toBeGreaterThan(40);
+    const sections = [...new Set(controls.map(row => row.section))];
+    for (const section of sections) {
+        await page.goto(`${workspace}#/system/${section}`);
+        const main = page.locator('#workspace-main');
+        await expect(layoutOf(page).locator(':scope > *').first()).toBeVisible();
+        for (const details of await main.locator('details:not([open]) > summary').all()) await details.click();
+        for (const { capability, role, name, row } of controls.filter(item => item.section === section)) {
+            // A name several rows share is looked up inside the row the table names.
+            const within = row ? main.locator('.operation').filter({ has: page.locator(`h3:text-is("${row}")`) }) : main;
+            const exact = new RegExp(`^${name.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}$`);
+            // A `dt` (term) and a `details` disclosure (group) have no name from content: the term's text, the summary's.
+            const control = role === 'term' ? within.getByRole('term').filter({ hasText: exact })
+                : role === 'group' ? within.locator('details').filter({ has: page.locator(':scope > summary', { hasText: exact }) })
+                    .or(within.getByRole('group', { name, exact: true }))
+                    : within.getByRole(role, { name, exact: true });
+            await expect(control.first(), `${capability}: ${section} · ${role} · "${name}"${row ? ` in "${row}"` : ''}`).toBeVisible();
+        }
+    }
+}
diff --git a/tests/browser/workspace_diagnostics_fixture.py b/tests/browser/workspace_diagnostics_fixture.py
index 9a47009..b55cf34 100644
--- a/tests/browser/workspace_diagnostics_fixture.py
+++ b/tests/browser/workspace_diagnostics_fixture.py
@@ -14,7 +14,11 @@ real log folder. Every route refuses a log folder outside the server root.
   more INFO records older still), ``active`` bytes into the active log,
   rotated copies ``prompt_manager.log.<n>`` of the listed sizes (fixed
   times), on POSIX a symlink ``prompt_manager.log.<n+1>`` to a file outside
-  the folder (``link``) and a user's ``prompt_manager.log.bak`` (``other``);
+  the folder (``link``) and a user's ``prompt_manager.log.bak`` (``other``).
+  ``{mode: "concept"}`` reproduces the concept's Logs sample (app.js 695)
+  for the comparison: the buffer holds only its four lines, the active log
+  is 1.4 MB with three rotated copies ("prompt_manager.log · 1.4 MB · rotated
+  copies: 3") and console logging is off, as the concept's toggle;
 - ``POST /__test__/logs/rotate`` rolls the copies over as the handler does
   (``.2`` → ``.3``, ``.1`` → ``.2``, a new ``.1``), so a reviewed plan no
   longer matches;
@@ -48,6 +52,10 @@ LEVEL_RECORDS = (
     ("09:30:03", logging.CRITICAL, "The database could not be opened"),
 )
 ROTATED_TIME = datetime.datetime(2026, 10, 25, 14, 2)
+# The concept's "prompt_manager.log · 1.4 MB · rotated copies: 3": the active
+# log stays under 1.45 MB while the server writes its own lines.
+CONCEPT_ACTIVE = int(1.4 * 1024 * 1024)
+CONCEPT_ROTATED = (3072, 2048, 1024)
 MAX_SEED_BYTES = 64 * 1024 * 1024
 DEFAULT_CONFIG = {
     "level": "INFO",
@@ -152,7 +160,25 @@ def register_diagnostics_commands(app, routes, api, root: Path):
         with manager._buffer_lock:
             manager._log_buffer.clear()
 
+    def seed_concept() -> None:
+        manager = _manager()
+        log_dir = folder()
+        manager.update_config({"console_logging": False})
+        with manager._buffer_lock:
+            manager._log_buffer.clear()
+        for index, (time_text, level, message) in enumerate(CONCEPT_RECORDS):
+            record = _record(time_text, level, message, index)
+            manager.add_to_buffer(record, record.getMessage())
+        with open(log_dir / ACTIVE, "ab") as handle:
+            handle.write(b"x" * CONCEPT_ACTIVE)
+        for number, size in enumerate(CONCEPT_ROTATED, start=1):
+            moment = ROTATED_TIME - datetime.timedelta(hours=number)
+            _touch(log_dir / f"{ACTIVE}.{number}", size, moment)
+
     def seed(data) -> None:
+        if data.get("mode") == "concept":
+            seed_concept()
+            return
         manager = _manager()
         log_dir = folder()
         with_records = data.get("records", True) is not False
diff --git a/tests/vendor/legacy-coverage.test.mjs b/tests/vendor/legacy-coverage.test.mjs
new file mode 100644
index 0000000..c1bf38d
--- /dev/null
+++ b/tests/vendor/legacy-coverage.test.mjs
@@ -0,0 +1,116 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { COLUMNS, CONTROL_EXEMPTIONS, STATUSES, declaredTitles, parseControl, parseCoverageTable, readCoverageTable,
+    rowProblems } from '../../tools/vendor/legacy-coverage.mjs';
+
+// TESTING.md "Legacy System capability coverage" (#249 System S12, #329): every legacy System capability names an
+// owner, a known status, a well-formed native control and a test its file really declares.
+
+const ROW = Object.freeze({ Capability: 'Clear/truncate logs', 'Legacy anchor': '`admin.html:915`', Owner: 'S12 Logs',
+    Status: 'covered', 'Native control': '`diagnostics` · button · "Clear all logs…"', Test: 'clears the logs (clear.spec.mjs)' });
+const declaring = source => ({ locate: file => `tests/browser/${file}`, read: () => source });
+
+test('every coverage row has an owner, a known status and a declared test', () => {
+    const rows = readCoverageTable();
+    assert.ok(rows.length >= 54, `the table lists ${rows.length} capabilities`);
+    for (const row of rows) {
+        assert.deepEqual(rowProblems(row), [], `TESTING.md:${row.line} ${row.Capability}`);
+        assert.ok(row.Owner.trim());
+        assert.ok(STATUSES.includes(row.Status));
+    }
+    assert.ok(rows.some(row => row.Status === 'kept in legacy') && rows.some(row => row.Status === 'approved removal'));
+    // A broken row fails: an empty owner, an unknown status, a test its file does not declare.
+    const [first] = rows;
+    assert.deepEqual(rowProblems({ ...first, Owner: '' }), ['no owner']);
+    assert.ok(rowProblems({ ...first, Status: 'done' }).includes('unknown status "done"'));
+    assert.match(rowProblems({ ...first, Test: first.Test.replace(/^(.+) \(/, '$1 again (') }).join(), /declares no test/);
+    assert.match(rowProblems({ ...first, Test: 'some title (missing.spec.mjs)' }).join(), /no test file missing\.spec\.mjs/);
+});
+
+test('a title that appears only in a comment does not count', () => {
+    const commented = [
+        "// test('clears the logs', async () => {});",
+        "/* test('clears the logs', async () => {}); */",
+        '/**',
+        " * it('clears the logs')",
+        ' */',
+        "const title = 'clears the logs';",
+        "test.describe('clears the logs', () => {});",
+    ].join('\n');
+    assert.equal(declaredTitles(commented, 'clear.spec.mjs').has('clears the logs'), false);
+    assert.deepEqual(rowProblems(ROW, declaring(commented)), ['clear.spec.mjs declares no test "clears the logs"']);
+    const declared = `${commented}\nfor (const theme of THEMES) {\n    test('clears the logs', async ({ page }) => {});\n}\n`;
+    assert.deepEqual(rowProblems(ROW, declaring(declared)), []);
+    // Escaped quotes, template literals, modifiers and a title on the next line are declarations too.
+    const titles = declaredTitles("test('a gate\\'s refusal', () => {});\ntest.only(`b`, () => {});\nit(\n    'c', () => {});",
+        'x.test.js');
+    assert.deepEqual([...titles], ["a gate's refusal", 'b', 'c']);
+    // A block comment that starts after code on a line, and a `//` or `/*` inside a string or a regular expression.
+    const trailing = [
+        "const url = 'http://host/*'; /* test('clears the logs', () => {});",
+        "test('clears the logs', () => {}); */",
+        "const pattern = /['\"`]\\/\\*/;",
+        "test('after the pattern', () => {});",
+    ].join('\n');
+    assert.deepEqual([...declaredTitles(trailing, 'x.spec.mjs')], ['after the pattern']);
+    // Python: only a real `def test_…` counts, never a commented one.
+    const python = ['# def test_report_lists_config_only_keys(self):', 'class T:', '    \"\"\"Example:', '',
+        '    def test_in_a_docstring(self):', '    \"\"\"', '    def test_other(self):', '        def test_nested():',
+        '            pass', 'def test_module():', '    pass', ''].join('\n');
+    assert.deepEqual([...declaredTitles(python, 'test_x.py')], ['test_other', 'test_module']);
+});
+
+test('a malformed native control cell fails', () => {
+    assert.deepEqual(parseControl('`diagnostics` · button · "Clear all logs…"'),
+        { section: 'diagnostics', role: 'button', name: 'Clear all logs…', row: null });
+    assert.deepEqual(parseControl('`maintenance` · button · "Review plan" · in "Duplicate prompt text"'),
+        { section: 'maintenance', role: 'button', name: 'Review plan', row: 'Duplicate prompt text' });
+    assert.equal(parseControl('—'), null);
+    for (const [cell, message] of [
+        ['diagnostics · button · "Clear all logs…"', /malformed/],
+        ['`diagnostics` · button · Clear all logs…', /malformed/],
+        ['`diagnostics` - button - "Clear all logs…"', /malformed/],
+        ['', /malformed/],
+        ['`logs` · button · "Clear all logs…"', /unknown System section "logs"/],
+        ['`diagnostics` · link · "Clear all logs…"', /unknown role "link"/],
+    ]) {
+        assert.throws(() => parseControl(cell), message, cell);
+        assert.match(rowProblems({ ...ROW, 'Native control': cell }, declaring("test('clears the logs', () => {});")).join(), message);
+    }
+    // Only a covered row names a control.
+    assert.deepEqual(rowProblems({ ...ROW, Status: 'kept in legacy' }, declaring("test('clears the logs', () => {});")),
+        ['a kept in legacy row names a native control']);
+    // The table itself must keep its six columns.
+    assert.throws(() => parseCoverageTable(`### Legacy System capability coverage\n\n| Capability | Owner |\n| --- | --- |\n`), /columns/);
+    assert.deepEqual(COLUMNS, ['Capability', 'Legacy anchor', 'Owner', 'Status', 'Native control', 'Test']);
+});
+
+test('a skipped test does not prove a capability', () => {
+    for (const modifier of ['skip', 'fixme', 'fail']) {
+        assert.deepEqual(rowProblems(ROW, declaring(`test.${modifier}('clears the logs', async () => {});`)),
+            ['clear.spec.mjs only skips "clears the logs"'], modifier);
+    }
+    for (const modifier of ['only', 'slow']) {
+        assert.deepEqual(rowProblems(ROW, declaring(`test.${modifier}('clears the logs', async () => {});`)), [], modifier);
+    }
+    // A running declaration beside a skipped one counts.
+    assert.deepEqual(rowProblems(ROW, declaring("test.skip('clears the logs', () => {});\ntest('clears the logs', () => {});")), []);
+});
+
+test('a covered row names its native control unless it is exempt', () => {
+    const source = declaring("test('clears the logs', () => {});");
+    assert.deepEqual(rowProblems({ ...ROW, 'Native control': '—' }, source), ['a covered row names no native control']);
+    for (const status of ['kept in legacy', 'approved removal']) {
+        assert.deepEqual(rowProblems({ ...ROW, Status: status, 'Native control': '—' }, source), [], status);
+    }
+    const [exempt] = Object.keys(CONTROL_EXEMPTIONS);
+    assert.deepEqual(rowProblems({ ...ROW, Capability: exempt, 'Native control': '—' }, source), []);
+    // Every exemption has a reason and names a covered row of the table that has no control.
+    const rows = readCoverageTable();
+    for (const [capability, reason] of Object.entries(CONTROL_EXEMPTIONS)) {
+        assert.ok(reason.length > 20, capability);
+        const row = rows.find(item => item.Capability === capability);
+        assert.ok(row, `${capability} is in the table`);
+        assert.deepEqual([row.Status, row['Native control']], ['covered', '—']);
+    }
+});
diff --git a/tools/vendor/legacy-coverage.mjs b/tools/vendor/legacy-coverage.mjs
new file mode 100644
index 0000000..46a807c
--- /dev/null
+++ b/tools/vendor/legacy-coverage.mjs
@@ -0,0 +1,215 @@
+// The legacy System capability coverage table (TESTING.md "Legacy System capability coverage", #249 System S12 #329):
+// every capability of the legacy admin and gallery pages names its owner, a status, the native control that replaces it
+// and a declared test. tests/vendor/legacy-coverage.test.mjs checks each row against the test files; the browser spec
+// `every covered legacy System capability has its native control` finds each covered row's control on its System page.
+import { readFileSync, existsSync } from 'node:fs';
+import { join, dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+export const ROOT = join(dirname(fileURLToPath(import.meta.url)), '../..');
+export const HEADING = '### Legacy System capability coverage';
+export const COLUMNS = Object.freeze(['Capability', 'Legacy anchor', 'Owner', 'Status', 'Native control', 'Test']);
+export const STATUSES = Object.freeze(['covered', 'kept in legacy', 'approved removal']);
+export const SECTIONS = Object.freeze(['overview', 'appearance', 'sources', 'integrations', 'tagging', 'maintenance', 'backups',
+    'diagnostics']);
+export const ROLES = Object.freeze(['button', 'combobox', 'switch', 'slider', 'spinbutton', 'textbox', 'group', 'status', 'term']);
+// Where a Test cell's file is looked up, in order.
+export const TEST_FOLDERS = Object.freeze(['tests/browser', 'tests/js', 'tests/vendor', 'tests']);
+const NONE = '—';
+/**
+ * Covered rows whose replacement is not on a System section, so they name no native control (`—`), each with why. Every
+ * other covered row must name one.
+ */
+export const CONTROL_EXEMPTIONS = Object.freeze({
+    'Gallery per-image auto-tag / review': 'owned by the Images selection bar (Auto-tag selected), not a System section',
+});
+
+/** Split a Markdown table row into its cells (a `|` inside backticks is not a separator). */
+function cells(line) {
+    const out = [];
+    let cell = '';
+    let code = false;
+    for (const char of line.trim().replace(/^\|/, '').replace(/\|$/, '')) {
+        if (char === '`') code = !code;
+        if (char === '|' && !code) {
+            out.push(cell.trim());
+            cell = '';
+        } else {
+            cell += char;
+        }
+    }
+    out.push(cell.trim());
+    return out;
+}
+
+/** The table's rows as objects keyed by COLUMNS, from the section that starts at HEADING. */
+export function parseCoverageTable(markdown) {
+    const lines = markdown.split('\n');
+    const start = lines.findIndex(line => line.trim() === HEADING);
+    if (start === -1) throw new Error(`TESTING.md has no "${HEADING}" section`);
+    const header = lines.findIndex((line, index) => index > start && line.trim().startsWith('|'));
+    if (header === -1 || lines.slice(start + 1, header).some(line => /^#{1,3} /.test(line))) {
+        throw new Error('The coverage section has no table');
+    }
+    const columns = cells(lines[header]);
+    if (columns.join('|') !== COLUMNS.join('|')) throw new Error(`The coverage table's columns are ${columns.join(', ')}`);
+    const rows = [];
+    for (let index = header + 2; index < lines.length && lines[index].trim().startsWith('|'); index += 1) {
+        const values = cells(lines[index]);
+        rows.push({ line: index + 1, ...Object.fromEntries(COLUMNS.map((column, at) => [column, values[at] ?? ''])) });
+    }
+    return rows;
+}
+
+/**
+ * A Native control cell: `` `<section>` · <role> · "<name>" ``, optionally ` · in "<row title>"` when the name is shared
+ * by several rows of the section → {section, role, name, row}; `—` → null; else it throws.
+ */
+export function parseControl(cell) {
+    if (cell === NONE) return null;
+    const match = /^`([a-z]+)` · ([a-z]+) · "([^"]+)"(?: · in "([^"]+)")?$/.exec(cell);
+    if (!match) throw new Error(`malformed native control "${cell}"`);
+    const [, section, role, name, row = null] = match;
+    if (!SECTIONS.includes(section)) throw new Error(`unknown System section "${section}"`);
+    if (!ROLES.includes(role)) throw new Error(`unknown role "${role}"`);
+    return { section, role, name, row };
+}
+
+/** A Test cell: `<title> (<file>)` → {title, file}. */
+export function parseTest(cell) {
+    const match = /^(.+) \(([\w.-]+\.(?:mjs|js|py))\)$/.exec(cell);
+    if (!match) throw new Error(`malformed test cell "${cell}"`);
+    return { title: match[1], file: match[2] };
+}
+
+// Modifiers that still run the test; `.skip`, `.fixme` and `.fail` do not prove the capability.
+const RUNS = new Set(['', 'only', 'slow']);
+// After these characters (or at the start) a `/` opens a regular expression, not a division.
+const REGEX_BEFORE = /[(,=:[!&|?{};+\-*%<>~^]$/;
+
+/** Where the string, template literal or regular expression opened by `source[start]` ends (its closing index), or -1. */
+function literalEnd(source, start) {
+    const quote = source[start];
+    let inClass = false;
+    for (let end = start + 1; end < source.length; end += 1) {
+        const at = source[end];
+        if (at === '\\') end += 1;
+        else if (quote === '/' && at === '[') inClass = true;
+        else if (quote === '/' && at === ']') inClass = false;
+        else if (at === quote && !inClass) return end;
+        // A quoted string or a regular expression never spans lines.
+        else if (at === '\n' && quote !== '`') return -1;
+    }
+    return -1;
+}
+
+/**
+ * JavaScript `source` with every comment blanked (newlines kept), wherever it starts on a line. Strings, template
+ * literals and regular expressions are skipped whole, so a `//` or `/*` inside them is not a comment.
+ */
+export function stripJsComments(source) {
+    let out = '';
+    let index = 0;
+    while (index < source.length) {
+        const char = source[index];
+        const next = source[index + 1];
+        if (char === '/' && next === '/') {
+            while (index < source.length && source[index] !== '\n') index += 1;
+            continue;
+        }
+        if (char === '/' && next === '*') {
+            const close = source.indexOf('*/', index + 2);
+            const stop = close === -1 ? source.length : close + 2;
+            out += source.slice(index, stop).replace(/[^\n]/g, ' ');
+            index = stop;
+            continue;
+        }
+        const opens = char === "'" || char === '"' || char === '`' || (char === '/' && REGEX_BEFORE.test(out.trimEnd() || '('));
+        const end = opens ? literalEnd(source, index) : -1;
+        if (end === -1) {
+            out += char;
+            index += 1;
+        } else {
+            out += source.slice(index, end + 1);
+            index = end + 1;
+        }
+    }
+    return out;
+}
+
+/** Python `source` with its comments and triple-quoted strings (docstrings) blanked, newlines kept. */
+export function stripPythonComments(source) {
+    return source.replace(/("""|''')[\s\S]*?\1|#[^\n]*/g, text => text.replace(/[^\n]/g, ' '));
+}
+
+/**
+ * The tests a source declares, title → whether it runs: a `test('…'` or `it('…'` call at a line's start (`.only` and
+ * `.slow` run; `.skip`, `.fixme` and `.fail` do not) in JavaScript, a `def test_…` at function or method indentation in
+ * Python. Comments, and Python docstrings, never count.
+ */
+export function declarations(source, file) {
+    const found = new Map();
+    const add = (title, runs) => found.set(title, found.get(title) || runs);
+    if (file.endsWith('.py')) {
+        for (const match of stripPythonComments(source).matchAll(/^(?: {4})?(?:async[ \t]+)?def[ \t]+(test_\w+)[ \t]*\(/gm)) {
+            add(match[1], true);
+        }
+        return found;
+    }
+    const declaration = /^[ \t]*(?:test|it)(?:\.(only|skip|fixme|fail|slow))?\(\s*(['"`])((?:\\.|(?!\2)[^\\])*)\2/gm;
+    for (const match of stripJsComments(source).matchAll(declaration)) add(match[3].replace(/\\(.)/g, '$1'), RUNS.has(match[1] ?? ''));
+    return found;
+}
+
+/** The titles of the tests a source declares and runs. */
+export function declaredTitles(source, file) {
+    return new Set([...declarations(source, file)].filter(([, runs]) => runs).map(([title]) => title));
+}
+
+/** The repository path of a Test cell's file, or null. */
+export function testFile(file, root = ROOT) {
+    for (const folder of TEST_FOLDERS) {
+        const path = join(root, folder, file);
+        if (existsSync(path)) return path;
+    }
+    return null;
+}
+
+/** Every problem of one row (empty: the row is sound). `locate(file)` finds a test file's path, `read(path)` reads it. */
+export function rowProblems(row, { root = ROOT, locate = file => testFile(file, root), read = path => readFileSync(path, 'utf8') } = {}) {
+    const problems = [];
+    if (!row.Capability) problems.push('no capability');
+    if (!row['Legacy anchor']) problems.push('no legacy anchor');
+    if (!row.Owner) problems.push('no owner');
+    if (!STATUSES.includes(row.Status)) problems.push(`unknown status "${row.Status}"`);
+    let control = null;
+    try {
+        control = parseControl(row['Native control']);
+    } catch (error) {
+        problems.push(error.message);
+    }
+    if (control && row.Status !== 'covered') problems.push(`a ${row.Status} row names a native control`);
+    if (row.Status === 'covered' && row['Native control'] === NONE && !Object.hasOwn(CONTROL_EXEMPTIONS, row.Capability)) {
+        problems.push('a covered row names no native control');
+    }
+    let test;
+    try {
+        test = parseTest(row.Test);
+    } catch (error) {
+        problems.push(error.message);
+        return problems;
+    }
+    const path = locate(test.file);
+    if (!path) problems.push(`no test file ${test.file}`);
+    else {
+        const runs = declarations(read(path), test.file).get(test.title);
+        if (runs === undefined) problems.push(`${test.file} declares no test "${test.title}"`);
+        else if (!runs) problems.push(`${test.file} only skips "${test.title}"`);
+    }
+    return problems;
+}
+
+/** The table read from TESTING.md. */
+export function readCoverageTable(root = ROOT) {
+    return parseCoverageTable(readFileSync(join(root, 'TESTING.md'), 'utf8'));
+}