[ThomasK33]

Why

The operator asked to work every deferred follow-up issue of agent-tty until none is left. This PR fixes #251. #235 made snapshot and screenshot report capturedAtSeq: -1 on a session that has printed nothing. record export on the same session did not match. WebM failed with exit 7 EXPORT_ERROR, and asciicast reported seq 0, the seq of an event that does not exist.

What changed

• An empty event log is a valid state for record export, as it is for snapshot and screenshot since fix: capture an empty screen on a session that has printed nothing #235.
• Asciicast: the header-only cast reports capturedAtSeq: -1 [asciicast.ts:generateAsciicast] [record-export.ts:resolveCapturedAtSeq].
• WebM: the two "at least one event" guards are gone [record-export.ts] [webm.ts:generateWebmExport]. An empty log gives a blank video of the session's size with capturedAtSeq: -1 and durationMs: 0. The ghostty-web replayWithTiming accepts targetSeq -1, as replayTo already does.
• RecordExportResultSchema.capturedAtSeq uses ReplaySeqSchema (an integer of at least -1), and recordingFilename accepts -1.
• Docs: docs/USAGE.md and the export, protocol, storage and ghostty-web READMEs. The ghostty-web README line about lastAppliedSeq >= 0 was stale since fix: capture an empty screen on a session that has printed nothing #235 and is fixed.

Behavior for CLI and JSON users

• record export --format asciicast on an empty log: capturedAtSeq is -1 (was 0). The default file is recording--1-asciicast.cast (was recording-0-asciicast.cast). The file content is unchanged.
• record export --format webm on an empty log: exit 0 with a blank WebM, capturedAtSeq: -1, durationMs: 0, and metadata.outputEventCount: 0. It failed with exit 7 EXPORT_ERROR before. The default file is recording--1-webm.webm.
• The JSON schema now allows capturedAtSeq: -1 in record export results. No error code changes. A session with at least one event behaves as before.

Verification

• test/integration/empty-session-capture.test.ts "exports a header-only asciicast and a blank WebM at seq -1" fails on main 71d1b0c (asciicast seq 0, WebM exit 7) and passes on this branch.
• Unit tests updated: webm (empty log exports at seq -1), asciicast (-1), artifactStorage (recordingFilename(-2) throws), golden envelopes (invalid seq is -2).
• Gates: typecheck, lint and format:check exit 0. Unit: 138 files, 1731 tests passed. Integration (4 shards): 332 of 336 passed and e2e (3 shards): 33 of 34 passed on a host with load average 37. The 5 failures were timeouts in files that do not reach record export (run, cli, wait-render, lifecycle, resize-demo). Rerun alone, those 5 files passed 165 of 165.
• Live run of the built CLI: 1 of 4 checks pass on main 71d1b0c and 4 of 4 on this branch. The checks: asciicast seq on an empty log, WebM to the default path, WebM with --out (SHA matches), and an asciicast of a session that printed (seq 0, unchanged). ffprobe reads the blank WebM as VP9 with 28 frames.

Closes #251

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Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: xhigh

[ThomasK33]

@codex review

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-03T06:43:18.824672Z	8fc3ca3	Manual request

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Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: 21b94e669b

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[ThomasK33]

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Codex Review: Didn't find any major issues. Keep it up!

Reviewed commit: 8fc3ca3055

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