docs: add vouched contributor handoff guide

[saphid]

Observed problem and reproduction

CONTRIBUTING.md explains what outside work the project is likely to accept, but vouched contributors do not have one current handoff standard for deciding when a PR is ready for another human to review. The missing guidance shows up as stale PR descriptions, incomplete proof, unresolved findings, and unclear scope or platform impact.

Cause

The relevant rules exist across repository policy and recurring review practice, but no single document joins them into a pre-review checklist for trusted contributors.

Change and boundary

This PR adds one file, CONTRIBUTING_VOUCHED.md. It covers scope selection, existing ownership boundaries, proof matched to risk, real-app UI evidence, current PR descriptions, evidence-backed review responses, and a final handoff check. It also links six merged examples as examples of framing and proof.

Non-goals

This PR does not change public contribution policy, product behavior, contracts, providers, clients, or connection modes. It does not add a discoverability link from CONTRIBUTING.md, prescribe a fixed PR size, or treat automated approval as merge authority.

Affected areas

Affected: contributor documentation only.

Unaffected: web, desktop, React Native mobile, SwiftUI mobile, all providers, contracts, server behavior, persistence, and local, remote, relay, and tunnel connections.

Validation

Current head: 8391dc069.

• CI=true vp i: passed.
• vp fmt CONTRIBUTING_VOUCHED.md --check: passed.
• git diff --check origin/main...HEAD: passed.
• git diff --name-only origin/main...HEAD: returned exactly CONTRIBUTING_VOUCHED.md.
• All six referenced example PRs were confirmed merged.
• GitHub checks on the current head passed for format/check, tests, server shards, Rust, release smoke, PR labeling, Cursor Bugbot, and Macroscope checks. Mobile preview, mobile native analysis, and [code]smith were skipped because the documentation-only paths did not trigger them.

Risks, untested paths, and known gaps

• The guide records current practice and will need updates when repository policy changes. Current AGENTS.md and maintainer direction remain authoritative.
• Discoverability remains limited until maintainers choose where to link the guide.
• No browser, simulator, device, or integrated-client run applies to this one-file documentation diff.
• The branch is mergeable and has automated approval. Automated approval is not human product approval.
• Known gaps: no human maintainer review or direction has been recorded.

Evidence

No product UI or interaction changes. Screenshots and video do not apply.

Owning issue and stack

No owning issue and no stacked PR. #8279 is a separate follow-up that can use this guide when it lands. Maintainer edits are enabled.

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[macroscopeapp]

Approvability

Verdict: Approved at 8391dc0

Macroscope's review found this PR approvable — This PR adds one focused Markdown handoff guide and does not alter application code, configuration, or production runtime behavior. Direct inspection and lightweight formatting validation are sufficient for this documentation-only change.

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[t3dotgg]

Note

🤖 GPT-5.6 Sol responding on behalf of Theo

We're closing this PR as we clean up the T3 Code backlog. Thank you for taking the time to put this together.

We do not need a separate active branch for this vouched-contributor handoff guide. It does not fix a current release, build, reliability, or contributor blocker.

If you believe we closed this in error, please reopen the PR and leave a comment explaining what we missed.