fix(backfill): Workers-AI timeout guard for Sync + re-land Docs reader restyle

[AndresL230]

Two independent changes, bundled per request so the stranded Docs restyle rides an already-open PR to main.

1. Timeout-guard Workers AI so a hung summarize can't wedge Sync GitHub

Problem. The admin Sync GitHub button sticks forever on "Contacting GitHub — taking inventory of PRs and issues…". POST /admin/backfill calls Workers AI (@cf/google/gemma-4-26b-a4b-it, a slow 26B model) synchronously in the request the browser waits on. The await ai.run(...) in makeWorkersAiSummarizer is unbounded: when the daily Neuron budget is exhausted or the model is overloaded, the call can hang indefinitely (never resolves, never rejects). The surrounding try/catch only handles throws, so a hang wedges the whole request — observed as POST /admin/backfill never completing (>2 min) with 0 summary rows written.

Fix.

• makeWorkersAiSummarizer races ai.run(...) against a timer (WORKERS_AI_TIMEOUT_MS, default 15s). A timeout rejects into the same catch, returns null, and the existing deterministic excerpt fallback fires — so the request always completes. Timeout is injectable (workersAiPrSummarizer(ai, timeoutMs?) / workersAiIssueSummarizer(ai, timeoutMs?)) for unit testing; clearTimeout in a finally leaves no pending timer on a healthy call.
• SUMMARY_BATCH_LIMIT 20 → 5, so each /admin/backfill returns quickly and the frontend auto-loop shows progress instead of one long stall.
• The catch's diagnostic console.error now also logs timeouts (visible in wrangler tail).

Test (TDD, failing-first). New workersAiSummarizer — timeout guard block: a fake ai whose run never resolves + a 50ms injected timeout must resolve to null / model='excerpt' within the timeout. Verified RED then GREEN.

2. Re-land the Docs reader restyle onto main

The Docs reader restyle + collapsible nav tree (originally PR #25) was accidentally merged into the already-merged feat/mywork-grid-seed-docs branch instead of main, so it never reached main. Its web-only commit (web/src/canopy.css, main.ts, markdown.ts, render.ts) is cherry-picked here. The stale backfill.ts on that branch — a pre-#23 revert — is deliberately not included.

Verification

• npm run build:web → ok · npm run typecheck → clean (worker + web) · npx vitest run --exclude '**/.claude/**' → 422 passed
• ⏳ Deployed-worker verification of the timeout path is pending (Workers AI can't run locally) — confirm on the deployed canopy worker via wrangler tail + a Sync click.

🤖 Generated with Claude Code

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c5da8b87-6b2c-410d-9c73-171dbac8cc09

📥 Commits

Reviewing files that changed from the base of the PR and between 1038be7 and b363101.

📒 Files selected for processing (6)

• src/tools/summarize.ts
• test/summarize.test.ts
• web/src/canopy.css
• web/src/main.ts
• web/src/markdown.ts
• web/src/render.ts

📝 Walkthrough

Walkthrough

Adds a bounded timeout (WORKERS_AI_TIMEOUT_MS) to Workers AI summarizer calls using Promise.race, falling back to null (and thus excerpt summarization) on timeout or failure. Both public summarizer wrappers gain an optional timeoutMs parameter. Backfill's SUMMARY_BATCH_LIMIT is lowered from 20 to 5. Tests added for timeout fallback behavior.

Changes

Workers AI timeout and backfill batching

Layer / File(s)	Summary
Timeout constant and race-based execution guard src/tools/summarize.ts	Adds WORKERS_AI_TIMEOUT_MS and races ai.run against a timeout, returning null on timeout/throw/malformed output, clearing the timer in finally.
Public wrapper signatures and batch limit reduction src/tools/summarize.ts, src/tools/backfill.ts	Updates workersAiPrSummarizer/workersAiIssueSummarizer to accept optional timeoutMs; lowers SUMMARY_BATCH_LIMIT from 20 to 5 with updated comments.
Timeout fallback tests test/summarize.test.ts	Adds tests simulating a hanging AI call, verifying summarizers return null and storage functions fall back to excerpt summaries within timeout.

Estimated code review effort: 2 (Simple) | ~12 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant SharedSummarizer
  participant AiRun
  participant TimeoutTimer

  Caller->>SharedSummarizer: workersAiPrSummarizer/IssueSummarizer(ai, timeoutMs)
  SharedSummarizer->>AiRun: ai.run(...)
  SharedSummarizer->>TimeoutTimer: start timer(timeoutMs)
  alt AiRun resolves first
    AiRun-->>SharedSummarizer: model output
    SharedSummarizer-->>Caller: parsed summary
  else Timer fires first
    TimeoutTimer-->>SharedSummarizer: timeout rejection
    SharedSummarizer-->>Caller: null (fallback to excerpt)
  end
  SharedSummarizer->>TimeoutTimer: clear timer (finally)

Loading

Possibly related PRs

• SaplingLearn/canopy#11: Both PRs modify the workersAi*Summarizer/shared summarizer logic in src/tools/summarize.ts.
• SaplingLearn/canopy#12: Both PRs modify the Workers AI summarizer to return null on unusable ai.run() results, with overlapping test changes.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title captures the main Workers-AI timeout/backfill fix, though the trailing docs restyle note appears unrelated.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/backfill-ai-timeout-guard

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	canopy	b363101	Commit Preview URL Branch Preview URL	Jul 07 2026, 06:20 AM

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/tools/summarize.ts`:
- Around line 137-176: The current timeout logic in summarize() only stops
waiting because Promise.race does not cancel ai.run, so timed-out Workers AI
calls can keep consuming capacity. Update the workersAiSummarizer flow to create
an AbortController, pass its signal through the ai.run(AWORKERS_AI_MODEL, ...)
AiOptions, and abort it when the timeout promise wins; keep the existing
catch/fallback behavior and ensure the timer is still cleared in finally.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 9b368762-968f-4a7c-aed9-7c6168673869

📥 Commits

Reviewing files that changed from the base of the PR and between b28f5e5 and 1038be7.

📒 Files selected for processing (3)

• src/tools/backfill.ts
• src/tools/summarize.ts
• test/summarize.test.ts