chore(marketing): skip Vercel builds that do not touch the site

[rynfar]

What

The marketing site's Vercel config gets an ignoreCommand: a build is skipped unless apps/marketing, packages/shared (its one workspace dependency), or the lockfile changed since that branch's last deployment.

Why

apps/marketing/vercel.ts has git deployments on and no ignore rule, so Vercel built a preview on every push to every pull request branch and a production build on every merge. On 2026-09-18 there were 39 pull requests, most pushed several times, for a site whose own code last changed five commits ago. The account hit Vercel's build rate limit: the Vercel check then failed on unrelated pull requests with a build-rate-limit link, previews sat "deploying" for 40 minutes, and the release workflow's hosted-app deploy timed out four times (#655).

The hosted app (apps/web) already has git deployments off and is deployed only by the release workflow, so it needs no change here.

How

git diff --quiet "${VERCEL_GIT_PREVIOUS_SHA:-HEAD^}" HEAD -- . ../../packages/shared ../../pnpm-lock.yaml ../../pnpm-workspace.yaml, run from the project root apps/marketing. Exit 0 skips the build. If the previous SHA is not in Vercel's shallow clone, git fails with a non-zero code, which builds: the safe default.

Verification

• Typecheck @t3tools/marketing: 0 errors; ignoreCommand is in @vercel/config's VercelConfig type. vp check clean.
• Not verified on Vercel: that needs this to land and a push that does not touch the site. Expect the Vercel check on the next unrelated pull request to read as skipped rather than building.

Not addressed here

The release workflow deployed the hosted app 11 times that day (4 scheduled, 7 manual). Those are real deploys, not waste, but they share the same quota; dispatching one nightly for a batch of merges rather than one per merge keeps it down.

Closes part of #655.

Model: Claude Fable 5.1, in Pylon via the Claude Code harness.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

[vercel]

Deployment failed for project pylon-marketing with the following error:

Resource is limited - try again in 24 hours (more than 100, code: "api-deployments-free-per-day").

Learn More: https://vercel.com/pylon-code?upgradeToPro=build-rate-limit

[rynfar]

Merging with the Vercel preview check red: it failed with build-rate-limit, the problem this change fixes, so it cannot go green before it lands. Every code check is green. To confirm afterwards: the Vercel check on the next pull request that does not touch apps/marketing, packages/shared or the lockfile should be skipped instead of building.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	14.0 KiB	13.9 KiB	−9 B (−0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	−3 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−6 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	13.9 KiB	14.0 KiB	+54 B (+0.4%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.8 KiB	+54 B (+0.8%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.8 KiB	58.9 KiB	+44 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	9	+1 (+12.5%)	21	✅

Baseline: fe0c286 · PR result: a400486 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 115.6 KiB
• Claude decoded thread snapshot: 116.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.