fix: preserve recordings when storage runs low

[richiemcilroy]

Summary

• Show native low-storage warnings before recording, including deep-link starts, and restore the editor if preflight fails.
• Sample free space and recording size every two seconds in one cancellable background task. Cache completed-fragment sizes with a bounded cache, reserve finalization space, and freeze the timer while saving.
• Fix muxer reader shutdown deadlocks without killing slow writers. Preserve original fragments and recover complete segments missing from the last manifest.
• Serialize and atomically replace Instant metadata, and stop upload tasks before exposing recovery after a local failure.

Verification

• Scoped GPUI and recording checks passed, including an isolated source snapshot with the committed GPUI dependency patch.
• GPUI recording (10), upload (11), library (14), and deep-link (16) tests passed. Coverage includes concurrent metadata updates, a partial write failure, upload cancellation, and recovery with stale recording state.
• cap-muxer (8) unit tests passed. The isolated PR snapshot passed all 27 cap-utils library tests, including growing files, a 1 GiB recording reserve, and the cache limit.
• All 9 out-of-process muxer integration tests passed against the rebuilt helper, including real encoded output, shutdown without stdin EOF, and preservation of a writer taking more than five seconds.
• Native dialogs and automatic low-storage stopping were verified on macOS; the live test preserved all 119 captured frames.
• A macOS benchmark of the actual monitor source with 10,000 fragments averaged 4.1 ms per cached sample over 200 samples, about 0.2% of one CPU core at the two-second interval. This is not a whole-app profile.
• Real Instant media recovered and fully decoded with complete and truncated fragments when manifest entries were all unaccepted, the manifest was corrupt JSON, or the manifest was missing.
• All 10 recording recovery unit tests passed. Scoped cap-utils and cap-recording Clippy checks passed.
• Root and GPUI formatting and the isolated diff check passed.

Scope and limitations

CI is not fully green: the macOS sync job failed the unchanged channel-drain timing test (55 ms versus a 50 ms budget); all 10 recovery tests passed in that job. The same timing test passed five local retries. Windows and Linux A/V sync jobs passed; the macOS job is being rerun on the same PR head (attempt 2). Other native CI remains separate from these results.
Only the 11 recording/storage files in this PR are included. Concurrent platform, release, camera, and web changes are excluded. Authenticated Instant uploads and Windows/Linux runtime behavior were not exercised here. The two existing documentation tests in untouched crates/utils/src/lib.rs fail in the isolated base snapshot; those unrelated examples are unchanged. No migrations or deployment changes.

Greptile Summary

The PR adds storage-aware recording preflight, monitoring, finalization, and recovery while preserving media when local saving cannot complete.

• Accounts for current recording size when reserving finalization space and automatically stopping.
• Rejects truncated M4S fragments while recovering complete fragments omitted from stale manifests.
• Adds atomic Instant metadata updates and safer muxer/upload shutdown behavior.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains; the recording-size monitor now reserves finalization space, and recovery rejects the truncated fragment state identified previously.

Important Files Changed

Filename	Overview
apps/desktop-gpui/src/session.rs	Coordinates the cancellable storage monitor with recording lifecycle transitions and low-storage stopping.
crates/utils/src/disk_space.rs	Measures recording size with a bounded fragment cache and reserves sufficient space for finalization.
apps/desktop-gpui/src/library.rs	Exposes interrupted Instant recordings only when initialization data and at least one structurally complete display fragment exist.
crates/recording/src/recovery.rs	Filters incomplete M4S tails and recovers complete fragments omitted from stale, corrupt, or missing manifests.
apps/desktop-gpui/src/recording.rs	Preserves local artifacts on low-storage failures and serializes Instant metadata and finalization updates.
crates/cap-muxer/src/main.rs	Revises muxer shutdown handling to avoid reader deadlocks without prematurely terminating slow writers.

_{Reviews (2): Last reviewed commit: "fix: reject incomplete fragments during ..." | Re-trigger Greptile}

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[richiemcilroy]

hey @greptileai, please re-review the PR

[richiemcilroy]

hey @greptileai, please re-review the PR