ci: run the perf budget on main pushes and on demand only

The wall-clock budget has under 2x margin on shared ubuntu runners, and
a red exact-head check blocks a merge that must never be rerun to green.
The job now runs on each push to main and on workflow_dispatch, not on
pull requests. TESTING.md says a red run on main means fix the code.

.github/workflows/test.yml

@@ -8,6 +8,7 @@ on:
     branches: [main]
   push:
     branches: [main]
+  workflow_dispatch:
 
 # Superseded PR pushes cancel their older run. Every main push gets its own
 # group (run_id), so no main commit's run is ever cancelled or dropped as pending.
@@ -148,7 +149,10 @@ jobs:
 
   perf-budget:
     # The reference wall-clock measurement (TESTING.md "Performance budgets").
+    # Shared-runner timing varies, so it never gates a pull request: it runs on
+    # each push to main and on demand. A red run on main means fix the code.
     name: perf budget
+    if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7

TESTING.md

@@ -143,14 +143,18 @@ A spec performance budget gets two tests:
 
 The `perf budget` job in `.github/workflows/test.yml` is the reference
 measurement: `ubuntu-latest`, one Python, no coverage, only the wall-clock tests.
+It runs on every push to `main` and on `workflow_dispatch`, never on pull
+requests, because shared-runner timing must not block a merge. Dispatch it on a
+branch to measure before merging.
 Shared Windows and macOS runners do not run them; the structural tests cover
 portability. Run it locally with
 `PROMPTMANAGER_PERF_BUDGET=1 python -m unittest tests.test_api_workspace_images.TestWorkspaceImages.test_filter_budget`
 and quote the printed p95 in the PR body.
 
-A red budget job means the code got slower: fix the code, or change the budget
-in the spec with a reason. Never rerun it to green. Whether `perf budget` is a
-required check is the maintainer's decision (`.github/branch-protection.json`).
+A red `perf budget` run on `main` means the code got slower: fix the code (or
+change the budget in the spec with a reason) in a follow-up PR. Never rerun it to
+green. It is not a required check, and it cannot be one while it skips pull
+requests (`.github/branch-protection.json`).
 
 ## Windows portability preflight