🤖 perf: document Report slowness and synthetic tape replay on the Profiling Xum page by ThomasK33 · Pull Request #5625 · coder/xum

ThomasK33 · 2026-10-04T16:27:16Z

Summary

Documents two merged perf features on the Profiling Xum page (docs/reference/profiling.mdx), and fixes one wrong runtime message.

Report slowness (🤖 perf: "Report slowness" local diagnostics bundle (F4) #5558): a new ## Report slowness section.
- How to run it: the palette command, a link to its shortcut on the keyboard shortcuts page, and xum api perf-reports create.
- Where the report goes: ~/.xum/perf/reports/<id>/.
- A table of every file in the report: snapshot.json, trace.json, environment.json, README.txt, captures/ with manifest.json, hangs.json and app-metrics.json. The last two are desktop only.
- What it never contains: tapes, chat content, prompts, tool payloads or environment variables.
- A warning that path redaction is partial, not anonymization: copied CPU profiles keep the folder names below ~ (🤖 perf: F4 "Report slowness" sanitizer follow-ups #5561).
- The "Report a performance problem" checklist now starts with this report.
- docs/config/keybinds.mdx keeps the shortcut and links here, so each fact has one home.
Tape replay (🤖 perf: replay synthetic session tapes through the desktop app with egress blocked (T3) #5612): a new "Replay a synthetic tape (contributors)" subsection.
- What make perf-tape-replay runs and where its output goes.
- It replays only synthetic fixtures. A warning says never to replay or commit real tapes.
- An accordion explains how replay stays offline. Replay runs only when XUM_E2E=1 and XUM_REPLAY_HARNESS=1 are set, and the test harness sets them, not the Makefile. The app blocks renderer requests, while the harness takes background network offline. Tape paths are checked for absolute local syntax only: .. and symlinks are accepted.
Refusal message (sessionTapeReplaySource.ts): it now says "Run make perf-tape-replay to use the isolated replay harness." The old text claimed the make target sets the markers. The existing test matches only /only inside the perf harness/, which is unchanged, so this PR adds no exact-copy test.

Validation

I ran the documented commands against a sandbox xum server with a temporary XUM_ROOT:
- perf-reports create with the experiment off fails with PRECONDITION_FAILED and the documented message.
- With the experiment on, it writes the documented layout: README.txt, captures/ with manifest.json, environment.json, snapshot.json and trace.json. Folders are 0700 and files 0600.
- The environment.json keys match the page, and the home path appears nowhere in the bundle.
- Two concurrent runs get CONFLICT with "a slowness report is already being written".
I rendered the page locally with the CI-pinned Mintlify and checked the new sections at desktop and 390 px widths. Both accordions expand.
make static-check-full passes, including mintlify broken-links. sessionTapeReplaySource.test.ts passes (25 tests).

Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: high • Cost: $30.02

…ss markers The E2E fixture sets XUM_E2E and the replay spec sets XUM_REPLAY_HARNESS. The refusal now points to make perf-tape-replay without naming the variables.

Adds a Report slowness section (bundle contents, limits, partial path redaction), a contributor section for make perf-tape-replay, and makes the report the first item of the performance issue checklist. The keybinds page links to the profiling page instead of repeating it.

mintlify · 2026-10-04T16:27:20Z

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ThomasK33 · 2026-10-04T16:27:25Z

@codex review

chatgpt-codex-connector · 2026-10-04T16:27:29Z

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-04T16:29:43.080418Z	`638fbc5`	Manual request
🔒 Security Review	✅ Completed 2026-10-04T16:32:44.464246Z	`638fbc5`	Manual request

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chatgpt-codex-connector · 2026-10-04T16:29:41Z

Codex Review: Didn't find any major issues. More of your lovely PRs please.

Reviewed commit: 638fbc580d

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chatgpt-codex-connector · 2026-10-04T16:32:43Z

🛡️ Codex Security Review · Automatically triggered

Security review completed. No security issues were found in this pull request.

Reviewed commit: 638fbc580d

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ThomasK33 added 2 commits October 4, 2026 16:17

fix(sessionTapes): stop claiming make perf-tape-replay sets the harne…

c09e444

…ss markers The E2E fixture sets XUM_E2E and the replay spec sets XUM_REPLAY_HARNESS. The refusal now points to make perf-tape-replay without naming the variables.

mintlify Bot deployed to staging - docs October 4, 2026 16:27 View deployment

ThomasK33 added this pull request to the merge queue Oct 4, 2026

Merged via the queue into main with commit a4ddcec Oct 4, 2026
58 of 61 checks passed

ThomasK33 deleted the perf/docs-report-and-replay branch October 4, 2026 16:57

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🤖 perf: document Report slowness and synthetic tape replay on the Profiling Xum page - #5625

🤖 perf: document Report slowness and synthetic tape replay on the Profiling Xum page#5625
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