perf(server): tighten pair probe budgets

[Adamulek123]

Summary

Pairing discovery probed up to 4 candidates strictly sequentially (worst ~10s), and the Tailscale cert-wait slept a full second after its final attempt.

What changed

• Cheap local checks (state file, pid) stay sequential to preserve precedence and error output; network probes run concurrently with the first precedence-ordered hit winning. Skip the retry sleep after the final cert-wait attempt.

Validation

• vp test run apps/server/src/cli/pair.test.ts — 26/26 pass.
• Package typecheck clean.

Summary by CodeRabbit

Bug Fixes

• Improved server pairing discovery across supported local environments.
• Pairing checks now run concurrently, reducing delays when multiple candidates are available.
• Improved selection of the correct available server when several candidates are detected.
• Invalid, oversized, non-JSON, or unsuccessful server responses are now rejected safely.
• Slow or unresponsive pairing requests time out instead of hanging.
• Pairing requests are canceled promptly when discovery is interrupted.
• Retry delays now occur only between Tailscale connection attempts.
• When no server is found, pairing provides details about the locations checked.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: pingdotgg/t3code/.coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: 83d020f9-1318-4722-8244-6884613603ef

📥 Commits

Reviewing files that changed from the base of the PR and between 6c5f68900894564f8f10e00ba0df10d1dcf10931 and 6947f22.

📒 Files selected for processing (1)

• apps/server/src/cli/pair.ts

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📝 Walkthrough

Walkthrough

The pair command bounds and validates environment descriptor responses before decoding. It probes live candidates concurrently, selects the first descriptor by precedence, cancels lower-priority probes, and avoids a final retry delay.

Changes

Pair target discovery

Layer / File(s)	Summary
Bounded descriptor probing apps/server/src/cli/pair.ts, apps/server/src/cli/pair.test.ts	Probes enforce a 64 KiB byte limit and a 2.5-second drain timeout. Non-2xx, non-JSON, oversized, invalid, and unreachable responses are treated as non-T3 results. Valid 2xx JSON responses use the shared decoder. Tests cover these cases and uppercase JSON media types.
Candidate collection and selection apps/server/src/cli/pair.ts, apps/server/src/cli/pair.test.ts	The command collects validated candidates, probes them concurrently, selects the first descriptor in precedence order, and interrupts lower-priority or cancelled probes. Tests cover overlap, status-based selection, and request abortion.
Tailscale retry timing apps/server/src/cli/pair.ts, apps/server/src/cli/pair.test.ts	The retry loop sleeps only when another attempt remains. Tests verify five attempts at one-second intervals without a final delay.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant PairCommand
  participant CandidateState
  participant EnvironmentProbes
  participant DescriptorDecoder
  PairCommand->>CandidateState: collect live candidates
  PairCommand->>EnvironmentProbes: start concurrent probes
  EnvironmentProbes->>DescriptorDecoder: decode bounded 2xx JSON response
  DescriptorDecoder-->>EnvironmentProbes: descriptor or failure
  EnvironmentProbes-->>PairCommand: probe results
  PairCommand->>EnvironmentProbes: cancel lower-priority probes
  PairCommand-->>PairCommand: select descriptor by precedence

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Suggested reviewers: bahlo, juliusmarminge

Merge Risk: ⚪ Minimal · up to 6947f

Pair discovery now bounds and validates responses, probes candidates concurrently while preserving precedence, cancels unnecessary probes, and avoids the final retry delay. These changes limit hangs and improve pairing responsiveness without a concrete merge-blocking risk.

🚥 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. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…
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.
Title check	✅ Passed	The title clearly summarizes the main change: tightening server pairing probe budgets.
Description check	✅ Passed	The description clearly states the problem, the concurrency and retry changes, and the validation results. It omits explicit Why and Checklist sections, but it provides the core information and remain…

✨ Finishing Touches

🧪 Generate unit tests (beta)

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[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The production pairing path now performs concurrent, cancelable server discovery and applies new response-size, media-type, status, timeout, and retry rules before selecting the server used for pairing. Although the change is well covered by tests and does not alter schemas or deployment configuration, its runtime and authentication-path impact is substantial enough for human review.

^{You can add or adjust custom eligibility rules. Learn more.}

Dismissing prior approval to re-evaluate 5c5e602

Dismissing prior approval to re-evaluate 6b91dc5