fix(indieauth,microsub,vc,conformance-target,examples): close LOW findings from issue #474 audit

[davidwkeith]

Summary

Closes #474. All HIGH and MEDIUM findings from the Workers-best-practices audit were already fixed by #477; this closes the 7 remaining LOW-severity findings:

• indieauth: createIndieAuth's route dispatch is now wrapped in try/catch — an unexpected exception (e.g. a D1 failure) returns a structured server_error OAuth response instead of crashing unhandled. Also added a runtime shape guard (isProfileInfo) so parseProfile no longer blind-casts the stored profile JSON column to ProfileInfo.
• microsub: handleFollow's poll-priming MICROSUB_QUEUE.send now runs via ctx.waitUntil instead of blocking the HTTP response — it's a cache-priming nicety, not something the client needs to wait on.
• vc: the signer cache (signerCache) is now scoped to each createVc() instance instead of a module-level global, so independently configured instances in the same isolate no longer silently share cache state — matching the composition contract's "instantiate multiple times, tested in isolation" rule.
• conformance-target: the request.body.cancel() floating promise in fetch() is now backgrounded via ctx.waitUntil; wrangler.jsonc's compatibility_date bumped from 2025-01-01 (~19 months stale) to 2026-07-01, matching the sibling examples/deploy-to-cloudflare/wrangler.jsonc.
• examples/deploy-to-cloudflare: the starter's fetch() routing dispatch is now wrapped in try/catch, since this file is copied wholesale into real deployed Workers (its own doc comment says as much) and previously had no crash guard at all.

Also updated issue #474's checklist to reflect the already-merged HIGH/MEDIUM items from #477 and check off the LOW items closed here.

Packages affected

@dwk/indieauth, @dwk/microsub, @dwk/vc, @dwk/conformance-target (private, no changeset), examples/deploy-to-cloudflare (private, no changeset)

Checklist

• Read the relevant spec(s) under spec/packages/ and updated them if
  behaviour changed — not applicable, all changes are internal
  robustness/isolation fixes with no observable protocol/behavior change
• Added/updated colocated tests (src/*.test.ts)
• Ran the local CI gate: pnpm lint && pnpm format:check && pnpm typecheck && pnpm build && pnpm test
• Added a changeset (pnpm changeset) if this touches a publishable
  package
• Updated catalog.json / conformance/status.json — not applicable, no new mountable worker or conformance-status change

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[davidwkeith]

Reviewed against CONTRIBUTING.md. Overall this is solid, low-risk hardening work — each fix is scoped to exactly what its changeset describes, and the return await fixes in indieauth/handler.ts and examples/deploy-to-cloudflare/src/index.ts are correct and necessary (without the explicit await, a rejection from the wrapped call would escape the enclosing try rather than being caught, since return promise inside a try doesn't implicitly await before leaving the block).

CONTRIBUTING.md conformance

• PR opened from the template with Summary / Packages affected / Checklist headings intact — good.
• Checklist: unticked items ("spec update", "catalog/status.json") each carry the required one-line reason instead of being deleted — good.
• Changesets: present for all three publishable packages touched (indieauth, microsub, vc); conformance-target and examples/deploy-to-cloudflare are correctly left out since both are private — good.
• Commit/PR title: fix(indieauth,microsub,vc,conformance-target,examples): … — lowercase type, no trailing period, comma-separated scopes. One minor nit: the scope convention is "package name minus the @dwk/ prefix"; conformance-target maps cleanly (@dwk/conformance-target), but examples doesn't correspond to any @dwk/-prefixed package (the folder's own package.json name is dwk-discovery-starter). Not worth blocking on — the meaning is still discoverable — but flagging in case the maintainer wants a more precise scope token for this repo's convention going forward.

Code — one inline suggestion

• packages/microsub/src/handler.ts:353 — the poll-priming queue send is now backgrounded via ctx.waitUntil but not .catch()'d, so a send failure is silently swallowed instead of logged (see inline comment for a concrete fix using the emit seam already used elsewhere in this handler). Not blocking.

Everything else — the indieauth shape guard (isProfileInfo), the per-instance vc signer cache, and the conformance-target wrangler.jsonc compatibility-date bump — looks correct and matches the composition contract's per-instance isolation rule. New tests look well-targeted (signer-cache isolation across two createVc() instances, malformed stored-profile shapes, the non-blocking follow-response test with an explicit waited array).

Note: CI (build-test, integration) was still in progress at review time — worth confirming green before merge.

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Generated by Claude Code

The build-test failure was @dwk/activitypub's mastodon-api.test.ts > publishStatus() escapes HTML metacharacters in both content and the CW summary — an assertion on a queued-delivery row count (expected +0 to be 1). This PR never touches activitypub/mastodon-api, and running that test 5× locally reproduces the failure ~1-in-5 with zero changes on my branch — it's a pre-existing flaky test (likely a timing/ordering issue in delivery queuing under load), not a regression from this PR. Re-ran the failed job (rerun_failed_jobs on run 30941737888); will keep watching.

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