fix(responses): record first-output timing for tool-only streams (carry #6259)

[lidge-jun]

Summary

Carries #6259 by @xyjk0511 onto current dev so it can get full hosted CI. The single commit is replayed unchanged and keeps its author.

A Responses turn that produces only a tool call never recorded a first-output time, so the request log showed output tokens with an empty TTFT. First-output detection only counted text and reasoning deltas. This PR also counts non-empty tool input:

• Native Responses SSE (firstOutputFromParsed in src/server/relay.ts) now counts non-empty response.function_call_arguments.delta and response.custom_tool_call_input.delta.
• The adapter bridge (src/bridge/sse.ts) counts a tool_call_delta with non-empty arguments.

Empty deltas, tool-start scaffolding, lifecycle events, and steer/inject control frames still do not start the timer, and the timestamp is still reported once. The dashboard guide and the transport docs now say the value is the first output the proxy saw, not the start of hidden reasoning or a decode-speed measurement. Whitespace-only tool input counts as output, the same length > 0 rule that text and reasoning already use.

Carried from #6259. Original author: @xyjk0511.

Co-authored-by: xyjk buchanliang@gmail.com

Verification

• I did not run local test suites or typecheck, on the project owner's explicit instruction. This is separate from the AGENTS.md resource exception. Hosted CI at the exact head of this PR is the only execution evidence. The original fork PR only ran the intake checks, so the full suite has not run on this change before.
• The carry is git cherry-pick f2771cfe5c..6f44cd646e onto dev 7b2deb8059. It applied without conflicts: 7 files, +64/-7, identical to fix: record first-output timing for tool-only Responses streams #6259.
• Static checks run locally: git diff --check, bun run scripts/privacy-scan.ts, and bun run structure:check pass. None of the touched files is in tests/fixtures/file-size-baseline.json. tool_call_delta.arguments is typed string in src/types/request.ts, so the new branch reads a defined field.
• New regression cases are in tests/adapters/bridge.test.ts and tests/server/response-log-inspection.test.ts, both existing files.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed.
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults. This change touches no auth, credential, or request-body logging path; it only changes when a timing hook fires.

Summary by CodeRabbit

• Improvements

  • First-output timing now includes non-empty function arguments and custom-tool input, so tool-only responses can register a first output.
  • Empty input fragments and tool-start notifications do not start the timer. Timing reflects the first output observed by the proxy, not hidden reasoning or exact model-decoding speed.

• Documentation

  • Updated dashboard and response-transport guides to explain first-output timing behavior.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-01T12:57:43.591978Z	3937885	PR opened

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📚 Code guidelines (2)

src/AGENTS.md — auto-discovered
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📥 Commits

Reviewing files that changed from the base of the PR and between 7b2deb8 and 3937885.

📒 Files selected for processing (7)

• docs-site/src/content/docs/guides/web-dashboard.md
• src/bridge/sse.ts
• src/server/relay.ts
• structure/transports/responses-wire-shapes.md
• structure/transports/responses.md
• tests/adapters/bridge.test.ts
• tests/server/response-log-inspection.test.ts

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📝 Walkthrough

Walkthrough

First-output timing now starts on nonempty function-argument and custom-tool-input deltas. Empty deltas and tool-start scaffolding do not start the timer. Tests and documentation cover these event rules.

Changes

First-output timing

Layer / File(s)	Summary
Recognize tool-input deltas src/bridge/sse.ts, src/server/relay.ts, tests/adapters/bridge.test.ts, tests/server/response-log-inspection.test.ts, structure/transports/responses.md, structure/transports/responses-wire-shapes.md, docs-site/src/content/docs/guides/web-dashboard.md	The bridge and relay treat nonempty function-argument and custom-tool-input deltas as first output. Tests check empty and non-string deltas, fragmented input, and one-shot callback behavior. Documentation describes which events start the timer and what the measurement represents.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 39378

No actionable merge-blocking risk is identified. The change adds first-output timing for nonempty tool-input deltas, with tests and documentation describing the behavior.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 4 files. (3 skipped: 3…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: recording first-output timing for Responses streams that contain only tool calls. The carry reference is additional context and does not redu…
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 4 files. (3 skipped: 3 unsupported.)

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[lidge-jun]

Maintainer integration record (MAINTAINERS.md, dev-only) — DRAFT from lane L3

• PR fix(responses): record first-output timing for tool-only streams (carry #6259) #6392, maintainer carry of fix: record first-output timing for tool-only Responses streams #6259 by @xyjk0511: fix(responses): record first-output timing for tool-only streams.
• Exact head: 39378850c0c6c940cd315e5d14cb1eec97db8024. Base: 7b2deb8059 (dev at carry time). git merge-tree against the current dev is clean.
• Hosted CI at this head: Cross-platform CI run 36864938011 passed on attempt 1 (pull_request). Jobs: test 1/4 through test 4/4, gates, structure gate, storage policy, docker smoke, api usage, docs site build, keyring and npm-global legs, ci. React Doctor and hygiene passed. enforce-target run 36864937854 passed. A second enforce-target run, re-queued by a label event, was still queued at the time of writing; check it before merging.
• Local suites: not run, on explicit owner instruction. The original fork PR fix: record first-output timing for tool-only Responses streams #6259 ran only intake checks, so this is the first full suite on the change.
• Review: the maintainer review on fix: record first-output timing for tool-only Responses streams #6259 (62/80) recommended landing it with the length > 0 rule as is, after aligning with dev. Whitespace-only tool input counts as output, the same rule text and reasoning already use. No open review threads.
• Security: n/a. This changes only when a timing hook fires; it touches no auth, credentials, or request-body logging.
• Attribution: the commit is authored by @xyjk0511. The squash carries Co-authored-by: xyjk <buchanliang@gmail.com>. After merge, close fix: record first-output timing for tool-only Responses streams #6259 with a link to this PR.