diff --git a/tests/browser/full-inspector.spec.mjs b/tests/browser/full-inspector.spec.mjs
index e4efc5a7..7bbd7979 100644
--- a/tests/browser/full-inspector.spec.mjs
+++ b/tests/browser/full-inspector.spec.mjs
@@ -144,9 +144,10 @@ test('panel matches the concept order and copy',async({page,request})=>{
     await expect(panel.locator('.meta-grid dt')).toHaveText(['Seed','Steps','CFG','Sampler','Scheduler','Model']);
     await expect(panel.locator('.meta-grid dd')).toHaveText(['9007199254740993','28','6.5','dpmpp_2m','karras','fixture-model.safetensors']);
     const footer=panel.locator('.detail-footer');
-    await expect(footer.locator('button')).toHaveText(['Send to ComfyUI','Prompt history']);
+    // #331 D139: every listed file's footer ends with Collections… (folder icon).
+    await expect(footer.locator('button')).toHaveText(['Send to ComfyUI','Prompt history','Collections…']);
     await expect(footer.locator('button.send')).toHaveAccessibleName(`Send prompt pair to ComfyUI: ${POSITIVE_TITLE}`);
-    await expect(footer.locator('button.send svg.icon')).toHaveCount(1);await expect(footer.locator('button:not(.send) svg.icon')).toHaveCount(1);
+    await expect(footer.locator('button.send svg.icon')).toHaveCount(1);await expect(footer.locator('button:not(.send) svg.icon')).toHaveCount(2);
     await expect(panel).not.toContainText(/prompt evidence|Recipe tags|Positive prompt tags/);
     // Execution recorded and embedded parameters (D21), with the extension chip naming an unverified format.
     reads.patch=data=>{for (const role of ['positive','negative']) data.prompts[role].source='execution';};
@@ -156,10 +157,11 @@ test('panel matches the concept order and copy',async({page,request})=>{
     await selectFile(page,'ambiguous.png');await expect(panel.locator('.prompt-section.positive .prompt-text')).toHaveText('embedded positive');
     await expect(panel.locator('span.chip.blue')).toHaveText('Embedded parameters');
     await expect(panel.locator('.panel-heading .chip')).toHaveText('File extension PNG');await expect(panel.locator('.panel-heading .chip .ca-visually-hidden')).toHaveText('File extension ');
-    await expect(panel.locator('.detail-footer button')).toHaveText(['Send to ComfyUI']);
-    // Unlinked: no badge, category, tags, pair or history.
+    await expect(panel.locator('.detail-footer button')).toHaveText(['Send to ComfyUI','Collections…']);
+    // Unlinked: no badge, category, tags, pair or history; the footer holds only Collections… (D139).
     reads.patch=null;await selectFile(page,'empty.png');await expect(panel.locator('.panel-heading h2')).toHaveText('empty.png');
-    expect(await panelStructure(panel)).toEqual({outer:['img.detail-cover','div.detail-inner'],
+    await expect(panel.locator('.detail-footer button')).toHaveText(['Collections…']);
+    expect(await panelStructure(panel)).toEqual({outer:['img.detail-cover','div.detail-inner','div.detail-footer'],
         inner:['div.panel-heading','p.small','section.prompt-section.positive','section.prompt-section.negative','dl.meta-grid']});
     await expect(panel.locator('.meta-grid dd')).toHaveText(Array(6).fill('Not recorded'));
     // Ambiguous saved association: the same honest absence.
@@ -210,7 +212,7 @@ test('pair send and history appear only with real roles and link',async({page,re
     await expect(panel.getByRole('button',{name:'Send prompt pair to ComfyUI: explicit-empty.png',exact:true})).toBeVisible();
     await expect(panel.getByRole('button',{name:'Prompt history',exact:true})).toHaveCount(0);
     await selectFile(page,'empty.png');await expect(panel.locator('.panel-heading h2')).toHaveText('empty.png');
-    await expect(panel.locator('.detail-footer')).toHaveCount(0);await expect(panel.getByRole('button',{name:/^Send prompt pair/})).toHaveCount(0);
+    await expect(panel.locator('.detail-footer button')).toHaveText(['Collections…']);await expect(panel.getByRole('button',{name:/^Send prompt pair/})).toHaveCount(0);
 });
 
 test('no provenance, raw or download controls in the side panel',async({page,request})=>{
@@ -238,8 +240,8 @@ test('viewer details hold provenance, raw records and downloads',async({page,req
     await page.setViewportSize({width:1600,height:1100});const reads=await patchInspection(page);
     await fullFixture(page,request);let details=await viewerDetails(page,'complete.png');
     // The panel content without the cover, D117's Copy settings summary after the facts, then the two disclosures,
-    // then the pair send and history buttons (D20).
-    expect(await viewerStructure(details)).toEqual({outer:['div','button.send','button'],
+    // then the pair send and history buttons (D20) and D139's Collections….
+    expect(await viewerStructure(details)).toEqual({outer:['div','button.send','button','button'],
         inner:['div.panel-heading','p.small','div.tags','section.prompt-section.positive','section.prompt-section.negative','div.tags','dl.meta-grid','button.settings-summary','details','details']});
     await expect(details.locator(':scope > div > button')).toHaveText('Copy settings summary');
     await expect(details.locator(':scope > div > button.settings-summary')).toHaveCSS('white-space','normal');
@@ -250,7 +252,7 @@ test('viewer details hold provenance, raw records and downloads',async({page,req
     await expect(details.locator(':scope > div > .tags').last().locator('span.chip')).toHaveText(['fixture','geometric']);
     await expect(details.locator('.meta-grid').first().locator('dd')).toHaveText(['9007199254740993','28','6.5','dpmpp_2m','karras','fixture-model.safetensors']);
     await expect(details.locator('summary')).toHaveText(['File & provenance','Workflow & raw metadata']);
-    await expect(details.locator(':scope > button')).toHaveText(['Send to ComfyUI','Prompt history']);
+    await expect(details.locator(':scope > button')).toHaveText(['Send to ComfyUI','Prompt history','Collections…']);
     await expect(details.locator(':scope > button.send')).toHaveAccessibleName(`Send prompt pair to ComfyUI: ${POSITIVE_TITLE}`);
     // File & provenance: the honest facts and the concept's "Prompt evidence" line; no per-fact source lines.
     const provenance=details.locator('details').first();await provenance.locator('summary').click();
@@ -275,9 +277,10 @@ test('viewer details hold provenance, raw records and downloads',async({page,req
     await expect(details.getByText('Prompt evidence: embedded parameters',{exact:true})).toBeVisible();
     await expect(details.locator('.panel-heading .chip')).toHaveText('File extension PNG');
     await expect(details.locator('details dl.meta-grid dd').nth(4)).toHaveText('PNG extension');await expect(details).not.toContainText('.PNG');
-    // No badge, no line; no resolved pair or link, no buttons after the details.
+    // No badge, no line; no resolved pair or link: after the details only D139's Collections….
     reads.patch=null;await page.keyboard.press('Escape');details=await viewerDetails(page,'empty.png');
-    expect((await viewerStructure(details)).outer).toEqual(['div']);
+    expect((await viewerStructure(details)).outer).toEqual(['div','button']);
+    await expect(details.locator(':scope > button')).toHaveText(['Collections…']);
     await details.getByText('File & provenance',{exact:true}).click();await expect(details).not.toContainText('Prompt evidence');
     // The history button leaves the viewer for the prompt's history.
     await page.keyboard.press('Escape');details=await viewerDetails(page,'complete.png');
diff --git a/tests/browser/inspector-concept.spec.mjs b/tests/browser/inspector-concept.spec.mjs
index 0a43d7f1..45c1b16a 100644
--- a/tests/browser/inspector-concept.spec.mjs
+++ b/tests/browser/inspector-concept.spec.mjs
@@ -45,10 +45,11 @@ function withCategoryScope(inventory) {
 }
 
 /**
- * Recorded inspector deviations only (spec §8, TESTING.md D3, D20–D22, D34, D38 and D117); everything else must
+ * Recorded inspector deviations only (spec §8, TESTING.md D3, D20–D22, D34, D38, D117 and D139); everything else must
  * equal production. `reference.viewerPlain` is the concept's own full details
  * with its tag chips made plain (D20), D117's summary button added and, under a coarse pointer, D34's targets, all at
- * runtime: the browser lays out what follows them, as the Images spec's removed toolbar items do.
+ * runtime: the browser lays out what follows them, as the Images spec's removed toolbar items do. D139's
+ * "Collections…" is drawn after Prompt history in both the concept's panel footer and its full details.
  */
 export function mapInspectorConcept(reference,{viewport}) {
     const {panel,viewerPlain,fileControls}=reference;
@@ -105,6 +106,22 @@ async function openProductionPanel(page,theme) {
     await settle(page);
 }
 
+/**
+ * #331 D139: production's "Collections…" after Prompt history in `selector`'s buttons, drawn in the concept as its own
+ * Prompt history button (no action) with the concept's folder icon (its Images filter chip's); returns an undo.
+ */
+async function withCollectionsButton(page,selector) {
+    await page.evaluate(selector=>{
+        const history=[...document.querySelectorAll(`${selector} > button`)].find(button=>button.textContent.includes('Prompt history'));
+        const button=history.cloneNode(false);
+        for(const key of Object.keys(button.dataset))delete button.dataset[key];
+        button.append(document.querySelector('.filter-row .chip > svg.icon').cloneNode(true),' Collections…');
+        history.after(button);(window.__collectionsButtons??=[]).push(button);
+    },selector);
+    await settle(page);
+    return async()=>{await page.evaluate(()=>{for(const button of window.__collectionsButtons??[])button.remove();delete window.__collectionsButtons;});};
+}
+
 /**
  * The concept's tag chips in the open viewer as plain `span.chip`s (D20), D34's coarse targets and D117's "Copy
  * settings summary" after the six facts (LI-4), drawn as the concept's own plain button (its "Download sample JSON",
@@ -122,8 +139,9 @@ async function plainViewerChips(page) {
         summary.textContent='Copy settings summary';summary.classList.add('settings-summary');
         document.querySelector('#viewer-details > div > dl.meta-grid').after(summary);window.__summaryButton=summary;
     });
-    await settle(page);
+    const restoreCollections=await withCollectionsButton(page,'#viewer-details');
     return async()=>{
+        await restoreCollections();
         await page.evaluate(()=>{for(const [span,button] of window.__plainChips)span.replaceWith(button);delete window.__plainChips;
             window.__summaryButton.remove();delete window.__summaryButton;});
         await restoreTargets();
@@ -162,7 +180,9 @@ async function viewerOf(page,concept,mutation=null) {
     return {viewerDetails,viewerPlain,fileControls};
 }
 async function inventory(page,concept=false) {
+    const restoreCollections=concept?await withCollectionsButton(page,'#image-inspector > .detail-footer'):null;
     const {panel}=await inspectorOf(page);
+    await restoreCollections?.();
     const {viewerDetails,viewerPlain,fileControls}=await viewerOf(page,concept);
     return concept?{panel,viewerDetails,viewerPlain,fileControls}:{panel,viewerDetails,fileControls};
 }
@@ -325,7 +345,7 @@ test('a recipe-linked image without recipe metadata shows its positive prompt me
     await expect(rows.first().locator('.chip .ca-visually-hidden')).toHaveText('Positive prompt category: ');
     await expect(rows.nth(1).locator('button.chip')).toHaveText(['minimal','warm_light','editorial']);
     await expect(rows.nth(1).locator('span.chip')).toHaveCount(0);
-    await expect(panelOf(page).locator('.detail-footer button')).toHaveText(['Send to ComfyUI','Prompt history']);
+    await expect(panelOf(page).locator('.detail-footer button')).toHaveText(['Send to ComfyUI','Prompt history','Collections…']);
 });
 
 // Task C3 (D88, #249 PR C): the concept's chip row is the image's own tags (`i.tags`, app.js a402). With those names
@@ -380,6 +400,13 @@ test('inspector comparison detects mutations',async({page})=>{
     expect(()=>assertInspectorMatch(reference,withoutSummary,viewport)).toThrow(/viewerDetails\.structure\.inner/);
     assertInspectorMatch(reference,await viewerMutated(),viewport);
 
+    // D139: Collections… is part of the mapped concept, so losing it is a difference.
+    const restoreButton=await mutate(page,{remove:['#image-inspector > .detail-footer > button:last-child']});
+    const withoutCollections=await measure();
+    expect(()=>assertInspectorMatch(reference,withoutCollections,viewport)).toThrow(/panel\.footer/);
+    await restoreButton();await settle(page);
+    assertInspectorMatch(reference,await measure(),viewport);
+
     await mutate(page,{remove:['#image-inspector > .detail-footer']});
     const domMutated=await measure();
     expect(()=>assertInspectorMatch(reference,domMutated,viewport)).toThrow(/panel\.footer/);
diff --git a/tests/browser/workspace-collections.spec.mjs b/tests/browser/workspace-collections.spec.mjs
index e731d599..233182d8 100644
--- a/tests/browser/workspace-collections.spec.mjs
+++ b/tests/browser/workspace-collections.spec.mjs
@@ -520,3 +520,134 @@ for (const theme of ['dark', 'light']) {
         await expect(row(page, 'Phone')).toBeVisible();
     });
 }
+
+// #331 D139 (design §8): the shared inspector's Collections… in the Images side panel and in the viewer.
+const panel = page => page.locator('#image-inspector');
+const collectionsDialog = page => page.getByRole('dialog', { name: 'Collections', exact: true });
+const choice = (page, name) => collectionsDialog(page).getByRole('checkbox', { name, exact: true });
+const newCollection = page => collectionsDialog(page).getByRole('textbox', { name: 'New collection', exact: true });
+
+async function membership(request, path) {
+    const [image] = (await (await request.get(`/prompt_manager/images/output?mode=workspace&q=${encodeURIComponent(path)}`)).json()).images;
+    const query = new URLSearchParams({ root_index: String(image.root_index), root_scope: image.root_scope, path: image.path });
+    const response = await request.get(`${API}/membership?${query}`);
+    await expect(response).toBeOK();
+    return (await response.json()).collection_ids;
+}
+
+test('Collections… in the side panel adds, removes and creates for one image (CUJ 6)', async ({ page, request }) => {
+    const manifest = await seed(request);
+    const { Landscapes, Experiments } = manifest.collections;
+    await page.goto(`${workspace}#/images`);
+    // The newest image, landscape_01, is the panel's.
+    await expect(panel(page).getByRole('heading', { level: 2 })).toHaveText('landscape_01.png');
+    const open = panel(page).getByRole('button', { name: 'Collections…', exact: true });
+    await expect(panel(page).locator('.detail-footer > button').last()).toHaveText('Collections…');
+    await open.click();
+    await expect(collectionsDialog(page)).toBeVisible();
+    await expect(choice(page, 'Landscapes')).toBeChecked();
+    await expect(choice(page, 'Experiments')).not.toBeChecked();
+    await expect(collectionsDialog(page).locator('label.tag-suggestion')).toHaveText(['Experiments', 'Landscapes']);
+    await expect(collectionsDialog(page).locator('.dialog-actions button')).toHaveText(['Cancel', 'Save']);
+    await choice(page, 'Landscapes').uncheck();
+    await choice(page, 'Experiments').check();
+    await newCollection(page).fill('Grids');
+    await collectionsDialog(page).getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(collectionsDialog(page)).toHaveCount(0);
+    await expect(toast(page)).toHaveText('Collections updated.');
+    await expect(open).toBeFocused();
+    await expect(row(page, 'Grids').locator('.nav-count')).toHaveText('1');
+    await expect(row(page, 'Landscapes').locator('.nav-count')).toHaveText('11');
+    await expect(row(page, 'Experiments').locator('.nav-count')).toHaveText('9');
+    const grids = (await listed(request)).find(item => item.name === 'Grids');
+    expect((await membership(request, 'landscape_01')).sort()).toEqual([Experiments.id, grids.id].sort());
+    expect(Landscapes.id).not.toBe(grids.id);
+    // The Images page lists the same files; the dialog opened again shows the new state.
+    await expect(imageCards(page)).toHaveCount(21);
+    await open.click();
+    await expect(choice(page, 'Grids')).toBeChecked();
+    await expect(choice(page, 'Experiments')).toBeChecked();
+    await expect(choice(page, 'Landscapes')).not.toBeChecked();
+    // Save without a change sends nothing.
+    let writes = 0;
+    page.on('request', request => { if (request.url().includes(`${API}/items`)) writes++; });
+    await collectionsDialog(page).getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(collectionsDialog(page)).toHaveCount(0);
+    expect(writes).toBe(0);
+});
+
+test('Collections… in the viewer keeps the viewer until it closes (CUJ 7)', async ({ page, request }) => {
+    const manifest = await seed(request);
+    await page.goto(`${workspace}#/collection/${manifest.collections.Landscapes.id}`);
+    await expect(imageCards(page)).toHaveCount(12);
+    await page.getByRole('button', { name: 'Open landscape_01.png', exact: true }).click();
+    const viewer = page.locator('#viewer-dialog[open]');
+    await expect(viewer.locator('#viewer-title')).toContainText('landscape_01.png');
+    await viewer.locator('#viewer-details').getByRole('button', { name: 'Collections…', exact: true }).click();
+    await expect(choice(page, 'Landscapes')).toBeChecked();
+    await choice(page, 'Landscapes').uncheck();
+    await collectionsDialog(page).getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(toast(page)).toHaveText('Collections updated.');
+    await expect(collectionsDialog(page)).toHaveCount(0);
+    // The viewer stays on the image; the page keeps listing it while the viewer is open.
+    await expect(viewer.locator('#viewer-title')).toContainText('landscape_01.png');
+    await expect(row(page, 'Landscapes').locator('.nav-count')).toHaveText('11');
+    await expect(imageCards(page)).toHaveCount(12);
+    await viewer.getByRole('button', { name: 'Close image viewer', exact: true }).click();
+    await expect(viewer).toHaveCount(0);
+    await expect(imageCards(page)).toHaveCount(11);
+    await expect(card(page, 'collections/landscape_01.png')).toHaveCount(0);
+});
+
+test('a failed membership read says so and Retry reads it again', async ({ page, request }) => {
+    await seed(request);
+    let failing = true;
+    await page.route(`**${API}/membership?*`, route => failing
+        ? route.fulfill({ status: 500, contentType: 'application/json', body: '{"success":false,"error":"Collections could not be read."}' })
+        : route.fallback());
+    await page.goto(`${workspace}#/images`);
+    await panel(page).getByRole('button', { name: 'Collections…', exact: true }).click();
+    await expect(collectionsDialog(page).getByRole('alert').first()).toHaveText('Collections could not be loaded.');
+    await expect(collectionsDialog(page).getByRole('checkbox')).toHaveCount(0);
+    await expect(collectionsDialog(page).getByRole('button', { name: 'Save', exact: true })).toHaveAttribute('aria-disabled', 'true');
+    failing = false;
+    await collectionsDialog(page).getByRole('button', { name: 'Retry', exact: true }).click();
+    await expect(choice(page, 'Landscapes')).toBeChecked();
+    await expect(collectionsDialog(page).getByRole('button', { name: 'Retry', exact: true })).toBeHidden();
+    // A failed write keeps the dialog with the current membership.
+    await page.route(`**${API}/items`, route => route.fulfill({ status: 500, contentType: 'application/json',
+        body: '{"success":false,"error":"The collection could not be changed."}' }));
+    await choice(page, 'Experiments').check();
+    await collectionsDialog(page).getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(collectionsDialog(page).getByRole('alert')).toHaveText('The collections could not be updated. Try again.');
+    await expect(choice(page, 'Experiments')).not.toBeChecked();
+    await expect(choice(page, 'Landscapes')).toBeChecked();
+});
+
+test('a file in no collection with no collections at all can start one', async ({ page }) => {
+    await page.goto(`${workspace}#/images`);
+    await panel(page).getByRole('button', { name: 'Collections…', exact: true }).click();
+    await expect(collectionsDialog(page)).toContainText('No collections yet. Name one below.');
+    await newCollection(page).fill('First');
+    await collectionsDialog(page).getByRole('button', { name: 'Save', exact: true }).click();
+    await expect(toast(page)).toHaveText('Collections updated.');
+    await expect(rows(page)).toHaveCount(1);
+    await expect(row(page, 'First').locator('.nav-count')).toHaveText('1');
+});
+
+for (const theme of ['dark', 'light']) {
+    test(`the Collections dialog fits 390x844 ${theme}`, async ({ page, request }) => {
+        await seed(request);
+        await page.setViewportSize({ width: 390, height: 844 });
+        await page.goto(`${workspace}#/images`);
+        await page.getByRole('combobox', { name: 'Theme', exact: true }).selectOption(theme);
+        await panel(page).getByRole('button', { name: 'Collections…', exact: true }).click();
+        await expect(choice(page, 'Landscapes')).toBeChecked();
+        const fits = await collectionsDialog(page).evaluate(dialog => {
+            const box = dialog.getBoundingClientRect();
+            return box.left >= 0 && box.right <= window.innerWidth && dialog.scrollWidth <= dialog.clientWidth;
+        });
+        expect(fits).toBe(true);
+        expect(await page.evaluate(() => document.documentElement.scrollWidth <= window.innerWidth)).toBe(true);
+    });
+}
diff --git a/tests/js/workspace-file-inspector.test.js b/tests/js/workspace-file-inspector.test.js
index 6371f59c..f0571719 100644
--- a/tests/js/workspace-file-inspector.test.js
+++ b/tests/js/workspace-file-inspector.test.js
@@ -363,3 +363,196 @@ test('the D117 wrap rule targets only the settings summary button', async () =>
     assert.deepEqual(rules.map(line => line.trim()), ['.ca-tools #viewer-details .settings-summary { white-space: normal; /* D117 */ }']);
     assert.doesNotMatch(css, /#viewer-details > div > button/);
 });
+
+// #331 D139 (design §8): the shared inspector's "Collections…" footer button and its checklist dialog.
+const collectionsDialog = await import('../../web/js/workspace/inspector-collections.mjs').catch(() => null);
+const dialogModule = () => { assert.ok(collectionsDialog, 'inspector-collections.mjs is not implemented'); return collectionsDialog; };
+const COLLECTION_SCOPE = 'a'.repeat(64);
+const FILE = {root_index:2, root_scope:COLLECTION_SCOPE, path:'a.png'};
+function collectionsStore({member = [3], membership, add, remove} = {}) {
+    const calls = [];
+    const store = {
+        calls,
+        collections:[{id:3, name:'LoRa testing', count:3, missing:0}, {id:5, name:'Portraits', count:1, missing:0}],
+        membership: async target => { calls.push(['membership', target]); return membership ? membership() : [...member]; },
+        add: async (where, items) => { calls.push(['add', where, items]); if (add) return add(where, items);
+            return {collection:{id:where.collectionId ?? 9, name:where.name ?? 'x'}, created:!!where.name, added:1, already:0, notFound:0}; },
+        remove: async (id, items) => { calls.push(['remove', id, items]); if (remove) return remove(id, items);
+            return {collection:{id, name:'x'}, removed:1}; },
+        settled: async () => ({}),
+    };
+    return store;
+}
+function footerButtons(f) {
+    return f.walk(f.container, n => n.tagName === 'button').map(n => n.textContent.trim());
+}
+test('inspector shows Collections… only for a rooted file with a store', async () => {
+    for (const variant of ['panel', 'full']) {
+        const f = mountedDom(), scope = createScope();
+        try {
+            const view = mountFileInspector(f.container, {sender:{open() {}}, parentScope:scope, variant, collections:collectionsStore()});
+            view.setState({loading:false, error:false, record:{...record(), historyTarget:'#/library/1'}});
+            const labels = footerButtons(f);
+            assert.ok(labels.includes('Collections…'), `${variant}: the button is offered`);
+            // After Prompt history, as the last footer action.
+            assert.equal(labels.at(-1), 'Collections…');
+            assert.equal(labels.at(-2), 'Prompt history');
+            const button = f.walk(f.container, n => n.tagName === 'button' && n.textContent.trim() === 'Collections…')[0];
+            assert.equal(button.children[0].tagName, 'svg', 'with the folder icon');
+            view.dispose();
+        } finally { scope.dispose(); f.restore(); }
+    }
+    // No store (Prompt library galleries, Inspect a file) or a file that is not a listed one: no button.
+    const local = await localRecord(localPng('Fox Render.png'));
+    for (const [shown, store] of [[record(), null], [local, collectionsStore()],
+        [{...record(), identity:{...record().identity, root_scope:null}}, collectionsStore()]]) {
+        const f = mountedDom(), scope = createScope();
+        try {
+            const view = mountFileInspector(f.container, {sender:{open() {}}, parentScope:scope, variant:'full', collections:store});
+            view.setState({loading:false, error:false, record:shown});
+            assert.ok(!footerButtons(f).includes('Collections…'));
+            view.dispose();
+        } finally { scope.dispose(); f.restore(); }
+    }
+});
+
+/** Open the Collections dialog over FILE; returns its nodes by role and helpers. */
+function openCollections(store, extra = {}) {
+    const {openCollectionsDialog} = dialogModule();
+    const f = mountedDom(), scope = createScope(), toasts = [], changes = [];
+    let dialog = null, closed = 0;
+    openCollectionsDialog({scope, collections:store, target:FILE, trigger:null, notify:text => toasts.push(text),
+        onChanged:change => changes.push(change), openDialog:args => { dialog = args; f.container.append(...args.nodes); },
+        closeDialog:() => { closed++; }, ...extra});
+    const settle = () => new Promise(resolve => setTimeout(resolve, 0));
+    const find = predicate => f.walk(f.container, predicate);
+    const boxes = () => find(n => n.tagName === 'input' && n.type === 'checkbox');
+    const button = text => find(n => n.tagName === 'button' && n.textContent === text)[0];
+    const text = () => find(n => n.tagName === 'p').map(n => n.textContent).filter(Boolean);
+    return {f, scope, toasts, changes, get dialog() { return dialog; }, get closed() { return closed; }, settle, find, boxes, button, text,
+        done() { scope.dispose(); f.restore(); }};
+}
+
+test('the Collections dialog loads the membership and lists every collection', async () => {
+    const store = collectionsStore();
+    const view = openCollections(store);
+    try {
+        assert.equal(view.dialog.title, 'Collections');
+        assert.ok(view.text().includes('Loading collections…'));
+        assert.equal(view.button('Save').getAttribute('aria-disabled'), 'true');
+        await view.settle();
+        assert.deepEqual(store.calls, [['membership', FILE]]);
+        const labels = view.find(n => n.tagName === 'label' && n.className === 'tag-suggestion');
+        assert.deepEqual(labels.map(label => label.textContent), ['LoRa testing', 'Portraits']);
+        assert.deepEqual(view.boxes().map(box => box.checked), [true, false]);
+        const field = view.find(n => n.tagName === 'input' && n.type !== 'checkbox')[0];
+        assert.equal(field.maxLength, 100);
+        assert.equal(view.find(n => n.tagName === 'label' && n.htmlFor === field.id)[0].textContent, 'New collection');
+        assert.deepEqual(view.find(n => n.className === 'dialog-actions')[0].children.map(n => n.textContent), ['Cancel', 'Save']);
+        assert.equal(view.button('Save').getAttribute('aria-disabled'), null);
+    } finally { view.done(); }
+});
+
+test('without collections the dialog says to name one', async () => {
+    const store = collectionsStore({member:[]});
+    store.collections = [];
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        assert.ok(view.text().includes('No collections yet. Name one below.'));
+        assert.equal(view.boxes().length, 0);
+    } finally { view.done(); }
+});
+
+test('a failed membership read offers Retry', async () => {
+    let failing = true;
+    const store = collectionsStore({membership:() => { if (failing) throw new TypeError('offline'); return [5]; }});
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        assert.ok(view.text().includes('Collections could not be loaded.'));
+        assert.equal(view.button('Retry').hidden, false);
+        assert.equal(view.boxes().length, 0);
+        assert.equal(view.button('Save').getAttribute('aria-disabled'), 'true');
+        failing = false;
+        view.button('Retry').fire('click');
+        await view.settle();
+        assert.deepEqual(view.boxes().map(box => box.checked), [false, true]);
+        assert.equal(view.button('Retry').hidden, true);
+    } finally { view.done(); }
+});
+
+test('Save sends the new name, each added and each removed collection, in that order', async () => {
+    const store = collectionsStore();
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        const [lora, portraits] = view.boxes();
+        lora.checked = false; portraits.checked = true;
+        view.find(n => n.tagName === 'input' && n.type !== 'checkbox')[0].value = '  Grids  ';
+        view.button('Save').fire('click');
+        await view.settle(); await view.settle();
+        assert.deepEqual(store.calls.slice(1), [
+            ['add', {name:'Grids'}, [FILE]],
+            ['add', {collectionId:5}, [FILE]],
+            ['remove', 3, [FILE]],
+        ]);
+        assert.equal(view.closed, 1);
+        assert.deepEqual(view.toasts, ['Collections updated.']);
+        assert.deepEqual(view.changes, [{added:[9, 5], removed:[3]}]);
+    } finally { view.done(); }
+});
+
+test('Save without a change sends nothing and closes', async () => {
+    const store = collectionsStore();
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        view.find(n => n.tagName === 'input' && n.type !== 'checkbox')[0].value = '   ';
+        view.button('Save').fire('click');
+        await view.settle();
+        assert.deepEqual(store.calls.map(call => call[0]), ['membership']);
+        assert.equal(view.closed, 1);
+        assert.deepEqual(view.toasts, []);
+        assert.deepEqual(view.changes, []);
+    } finally { view.done(); }
+});
+
+test('a failed Save keeps the dialog, says so and shows the current membership', async () => {
+    let reads = 0;
+    const store = collectionsStore({membership:() => (reads++ ? [5] : [3]),
+        remove:() => { throw Object.assign(new Error('x'), {status:500}); }});
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        const [lora, portraits] = view.boxes();
+        lora.checked = false; portraits.checked = true;
+        view.button('Save').fire('click');
+        // While it saves, × and Escape keep the dialog and Save is busy.
+        assert.equal(view.dialog.canClose(), false);
+        assert.equal(view.button('Save').getAttribute('aria-disabled'), 'true');
+        for (let index = 0; index < 4; index++) await view.settle();
+        assert.equal(view.closed, 0);
+        assert.deepEqual(view.toasts, []);
+        const alert = view.find(n => n.getAttribute?.('role') === 'alert')[0];
+        assert.equal(alert.textContent, 'The collections could not be updated. Try again.');
+        // The add went through: the page hears about it; the list shows what the server holds now.
+        assert.deepEqual(view.changes, [{added:[5], removed:[]}]);
+        assert.deepEqual(view.boxes().map(box => box.checked), [false, true]);
+        assert.equal(view.dialog.canClose(), true);
+        assert.equal(view.button('Save').getAttribute('aria-disabled'), null);
+    } finally { view.done(); }
+});
+
+test('a name the store cannot take fails without a request', async () => {
+    const store = collectionsStore();
+    const view = openCollections(store);
+    try {
+        await view.settle();
+        view.find(n => n.tagName === 'input' && n.type !== 'checkbox')[0].value = 'bad\u0001name';
+        view.button('Save').fire('click');
+        for (let index = 0; index < 3; index++) await view.settle();
+        assert.deepEqual(store.calls.filter(call => call[0] !== 'membership'), []);
+        assert.equal(view.find(n => n.getAttribute?.('role') === 'alert')[0].textContent, 'The collections could not be updated. Try again.');
+    } finally { view.done(); }
+});
diff --git a/web/js/workspace/file-inspector.mjs b/web/js/workspace/file-inspector.mjs
index 9a868a8f..0611b676 100644
--- a/web/js/workspace/file-inspector.mjs
+++ b/web/js/workspace/file-inspector.mjs
@@ -8,6 +8,7 @@ import { showWorkspaceToast } from './toast.mjs';
 import { openCopyFallback } from './workspace-dialogs.mjs';
 import { displayPreferences } from './preferences.mjs';
 import { fallBackToOriginal, thumbnailSource } from './thumbnail-support.mjs';
+import { openCollectionsDialog } from './inspector-collections.mjs';
 
 const RAW_KEYS = ['prompt', 'workflow', 'parameters', 'comfyassets_prompt_pairs'];
 const RAW_LIMIT = 'Raw metadata exceeds the response limit. Download the original file to inspect it externally.';
@@ -204,7 +205,12 @@ function prefixedChip(prefix, text) {
 /** D124: the inspector's line while "Load metadata on selection" is off. */
 export const DEFERRED_TEXT = 'Metadata loads when you ask for it.';
 
-export function mountFileInspector(container, {api, sender, parentScope, variant, inline = false, promptContext = '', onTagFilter, onRetry, onRefresh, onLoad, onInteraction = () => {}, copyFallback = openCopyFallback}) {
+/**
+ * #331 D139: with the client store `collections`, a listed file's footer ends with "Collections…", which opens its
+ * collections checklist; `onCollectionsChanged({added, removed})` hears the confirmed changes.
+ */
+export function mountFileInspector(container, {api, sender, parentScope, variant, inline = false, promptContext = '', onTagFilter, onRetry, onRefresh, onLoad, onInteraction = () => {}, copyFallback = openCopyFallback,
+    collections = null, onCollectionsChanged = () => {}}) {
     if (parentScope.signal.aborted) return {setState() {}, dispose() {}};
     const scope = childScope(parentScope);
     let contentScope;
@@ -300,6 +306,14 @@ export function mountFileInspector(container, {api, sender, parentScope, variant
             });
             footer.append(history);
         }
+        const member = collections ? revealTarget(record.identity) : null;
+        if (member) {
+            const button = createButton('');
+            button.append(createWorkspaceIcon('folder'), ' Collections…');
+            contentScope.listen(button, 'click', () => openCollectionsDialog({scope, collections, target:member, trigger:button,
+                onChanged:onCollectionsChanged}));
+            footer.append(button);
+        }
         if (!full && footer.childNodes.length) container.append(footer);
     }
     /**
diff --git a/web/js/workspace/images.mjs b/web/js/workspace/images.mjs
index aaa13d9c..aed1cdf0 100644
--- a/web/js/workspace/images.mjs
+++ b/web/js/workspace/images.mjs
@@ -279,7 +279,14 @@ export function mountImages(main, api, parentScope, {embedded = false, fetchPage
         onSourceChanged:refreshInspectionCollection});
     if (bar) main.append(bar.element);
     main.append(body);
+    // #331 D139: a change the inspector or the viewer confirmed that touches the open collection lists it again; the
+    // viewer reports only once it closes.
+    const inspectorCollections = embedded ? null : collections;
+    const collectionsChangedBy = ({added, removed}) => {
+        if (filters.collection && [...added, ...removed].includes(Number(filters.collection))) collectionChanged();
+    };
     const mediaViewer = createMediaViewer({api,container:main,parentScope:scope,inspectionController:inspection,sender,
+        collections:inspectorCollections,onCollectionsChanged:collectionsChangedBy,
         onSelect:image => {if (selection !== imageKey(image)) inspect(image);else inspection.select(image);},
         onRefresh:refreshInspectionCollection,onClose:scheduleLoad,onRestoreFocus:image => {
             const index = state?.items.findIndex(entry => imageKey(entry) === imageKey(image));
@@ -295,7 +302,8 @@ export function mountImages(main, api, parentScope, {embedded = false, fetchPage
         selection = imageKey(image);
         for (const video of details.querySelectorAll('video')) releaseVideo(video);
         detailInspector = mountFileInspector(details, {sender, parentScope:scope, variant:'panel',
-            onTagFilter:embedded ? undefined : filterByTag, onRetry:() => inspection.retry(), onLoad:() => inspection.load(), onRefresh:refreshInspectionCollection});
+            onTagFilter:embedded ? undefined : filterByTag, onRetry:() => inspection.retry(), onLoad:() => inspection.load(), onRefresh:refreshInspectionCollection,
+            collections:inspectorCollections, onCollectionsChanged:collectionsChangedBy});
         detailInspector.setState(inspection.state);
         inspection.select(image);
         for (const [key, card] of rendered) markSelected(card, key === selection);
diff --git a/web/js/workspace/inspector-collections.mjs b/web/js/workspace/inspector-collections.mjs
new file mode 100644
index 00000000..a7b780fc
--- /dev/null
+++ b/web/js/workspace/inspector-collections.mjs
@@ -0,0 +1,159 @@
+/**
+ * The shared inspector's "Collections…" dialog (#331 D139, design §8), beyond the concept: one listed file's
+ * collections as a checklist in the sidebar's order, a New collection field, then Cancel and Save.
+ *
+ * - The file's membership is read when the dialog opens ("Loading collections…"); a failed read says "Collections
+ *   could not be loaded." with Retry, and Save waits for a read that worked.
+ * - Each row is the concept's checkbox row (`label.tag-suggestion`, app.js a1128). With no collection the list says
+ *   "No collections yet. Name one below."
+ * - Save sends one request per change, in order: the new name, each newly checked collection, each unchecked one.
+ *   Nothing changed sends nothing and closes. All sent: the dialog closes with "Collections updated.". A failure keeps
+ *   it open with "The collections could not be updated. Try again." and the membership read again; the changes that
+ *   went through still reach `onChanged({added, removed})` (collection ids), as a full success does.
+ */
+import { createButton } from '../shared/toolkit/core.js';
+import { closeWorkspaceDialog, field, openContentDialog } from './workspace-dialogs.mjs';
+import { showWorkspaceToast } from './toast.mjs';
+import { COLLECTIONS_UPDATED_TOAST, MAX_COLLECTION_NAME_LENGTH, MEMBERSHIP_FAILED_TEXT, MEMBERSHIP_LOADING_TEXT,
+    NO_COLLECTIONS_TEXT, UPDATE_FAILED_TEXT, normalizeCollectionName } from './collections.mjs';
+
+export const COLLECTIONS_DIALOG_TITLE = 'Collections';
+export const NEW_COLLECTION_LABEL = 'New collection';
+
+function el(tag, text, className) {
+    const node = document.createElement(tag);
+    if (text !== undefined) node.textContent = text;
+    if (className) node.className = className;
+    return node;
+}
+
+/**
+ * Open the dialog for `target` (`{root_index, root_scope, path}`) with the client store `collections`. `openDialog`
+ * and `closeDialog` are the dialog seams; `notify` the toast.
+ */
+export function openCollectionsDialog({ scope, collections, target, trigger = null, notify = showWorkspaceToast, onChanged = () => {},
+    openDialog = openContentDialog, closeDialog = closeWorkspaceDialog }) {
+    const local = new AbortController();
+    const active = () => !scope.signal.aborted && !local.signal.aborted;
+    let member = null, saving = false;
+    const status = el('p', '', 'small');
+    const retry = createButton('Retry');
+    const list = el('div');
+    list.setAttribute('role', 'group');
+    list.setAttribute('aria-label', COLLECTIONS_DIALOG_TITLE);
+    const input = el('input');
+    input.value = '';
+    input.maxLength = MAX_COLLECTION_NAME_LENGTH;
+    input.autocomplete = 'off';
+    const problem = el('p', '', 'small');
+    problem.setAttribute('role', 'alert');
+    problem.hidden = true;
+    const actions = el('div', undefined, 'dialog-actions');
+    const cancel = createButton('Cancel');
+    const save = createButton('Save', 'ca-primary');
+    actions.append(cancel, save);
+    const blocked = () => member === null || saving;
+    const paintSave = () => {
+        if (blocked()) save.setAttribute('aria-disabled', 'true');
+        else save.removeAttribute('aria-disabled');
+    };
+    retry.addEventListener('click', () => load());
+    cancel.addEventListener('click', () => { if (!saving) closeDialog(); });
+    save.addEventListener('click', () => { if (!blocked()) submit(); });
+
+    /** One checkbox row per collection, checked where the file is a member. */
+    function renderList() {
+        list.replaceChildren();
+        if (!collections.collections.length) {
+            list.append(el('p', NO_COLLECTIONS_TEXT, 'small'));
+            return;
+        }
+        for (const item of collections.collections) {
+            const row = el('label', undefined, 'tag-suggestion');
+            const box = el('input');
+            Object.assign(box, { type: 'checkbox', id: `collection-choice-${item.id}`, checked: member.has(item.id) });
+            box.dataset.collectionId = String(item.id);
+            row.htmlFor = box.id;
+            row.append(box, el('span', item.name));
+            list.append(row);
+        }
+    }
+    function showStatus(text, failed) {
+        status.textContent = text;
+        status.setAttribute('role', failed ? 'alert' : 'status');
+        status.hidden = !text;
+        retry.hidden = !failed;
+    }
+    async function load() {
+        member = null;
+        paintSave();
+        list.replaceChildren();
+        showStatus(MEMBERSHIP_LOADING_TEXT, false);
+        try {
+            const ids = await collections.membership(target);
+            if (!active()) return;
+            member = new Set(ids);
+            showStatus('', false);
+            renderList();
+        } catch {
+            if (!active()) return;
+            showStatus(MEMBERSHIP_FAILED_TEXT, true);
+        }
+        paintSave();
+    }
+    /** The requests Save sends, in order; null when the new name cannot be a collection name. */
+    function plan() {
+        const typed = input.value.trim();
+        const name = typed ? normalizeCollectionName(typed) : '';
+        if (name === null) return null;
+        const steps = name ? [{ add: { name } }] : [];
+        const boxes = [...list.children].map(row => row.children?.[0]).filter(box => box?.dataset?.collectionId);
+        for (const box of boxes) {
+            const id = Number(box.dataset.collectionId);
+            if (box.checked && !member.has(id)) steps.push({ add: { collectionId: id } });
+        }
+        for (const box of boxes) {
+            const id = Number(box.dataset.collectionId);
+            if (!box.checked && member.has(id)) steps.push({ remove: id });
+        }
+        return steps;
+    }
+    async function submit() {
+        problem.textContent = '';
+        problem.hidden = true;
+        const steps = plan();
+        if (steps?.length === 0) { closeDialog(); return; }
+        saving = true;
+        paintSave();
+        const added = [], removed = [];
+        let failed = steps === null;
+        for (const step of steps ?? []) {
+            try {
+                if (step.add) added.push((await collections.add(step.add, [target])).collection.id);
+                else removed.push((await collections.remove(step.remove, [target])).collection.id);
+            } catch {
+                failed = true;
+                break;
+            }
+            if (!active()) return;
+            if (step.add?.name) input.value = '';
+        }
+        if (!active()) return;
+        saving = false;
+        if (added.length || removed.length) onChanged({ added, removed });
+        if (!failed) {
+            closeDialog();
+            notify(COLLECTIONS_UPDATED_TOAST);
+            return;
+        }
+        problem.textContent = UPDATE_FAILED_TEXT;
+        problem.hidden = false;
+        // A collection deleted meanwhile is re-read by the store; the list then shows what the server holds.
+        await collections.settled();
+        if (active()) await load();
+    }
+    showStatus('', false);
+    openDialog({ scope, title: COLLECTIONS_DIALOG_TITLE, trigger, canClose: () => !saving, onClose: () => local.abort(),
+        nodes: [status, retry, list, field(NEW_COLLECTION_LABEL, input, 'collection-new'), problem, actions] });
+    load();
+}
diff --git a/web/js/workspace/media-viewer.mjs b/web/js/workspace/media-viewer.mjs
index 834c9957..05e16685 100644
--- a/web/js/workspace/media-viewer.mjs
+++ b/web/js/workspace/media-viewer.mjs
@@ -19,7 +19,12 @@ function element(tag, className, text) {
     return node;
 }
 
-export function createMediaViewer({api,container,parentScope,inspectionController,sender,onSelect,onRefresh,onRestoreFocus,onClose,adapter = rootedFileAdapter}) {
+/**
+ * #331 D139: with the client store `collections`, the viewer's inspector offers "Collections…"; the changes it confirms
+ * reach `onCollectionsChanged({added, removed})` once the viewer closes, so the viewer keeps its place while open.
+ */
+export function createMediaViewer({api,container,parentScope,inspectionController,sender,onSelect,onRefresh,onRestoreFocus,onClose,adapter = rootedFileAdapter,
+    collections = null,onCollectionsChanged = () => {}}) {
     const scope = createScope();
     let active = null, retryVersion = 0;
     const dispose = () => scope.dispose();
@@ -36,7 +41,7 @@ export function createMediaViewer({api,container,parentScope,inspectionControlle
         active?.close(false);
         const {items,selectedKey,trigger = document.activeElement} = options;
         let mounted = false, initial, entry, currentKey, viewer = null, withoutViewer = false, mediaScope = null, closed = false;
-        let originalDownload = null, inspectionState = inspectionController.state;
+        let originalDownload = null, inspectionState = inspectionController.state, collectionChanges = null;
         const session = createViewerSession({adapter,items,initialKey:selectedKey,onChange:(state,selected) => {
             if (!mounted) { initial = [state,selected]; return; }
             update(state,selected);
@@ -99,7 +104,11 @@ export function createMediaViewer({api,container,parentScope,inspectionControlle
         const localSender = {open(roles,trigger) {session.stop();sender.open(roles,trigger);}};
         const inspector = mountFileInspector(details,{api,sender:localSender,parentScope:local,variant:'full',onInteraction:() => session.stop(),onRetry:() => inspectionController.retry(),
             onLoad:() => inspectionController.load?.(),
-            onRefresh:onRefresh ? () => { closeViewer();onRefresh(); } : undefined});
+            onRefresh:onRefresh ? () => { closeViewer();onRefresh(); } : undefined,collections,
+            onCollectionsChanged:({added,removed}) => {
+                collectionChanges ??= {added:[],removed:[]};
+                collectionChanges.added.push(...added);collectionChanges.removed.push(...removed);
+            }});
         function closeViewer(restore = true) {
             if (closed) return;
             closed = true;active = null;local.dispose();
@@ -108,6 +117,7 @@ export function createMediaViewer({api,container,parentScope,inspectionControlle
                 else onRestoreFocus?.(entry);
             }
             if (!scope.signal.aborted) onClose?.();
+            if (collectionChanges && !scope.signal.aborted) onCollectionsChanged(collectionChanges);
         }
         active = {close:closeViewer,stop:() => session.stop()};
         local.cleanup(() => {