feat: parse decrypted Antigravity CLI trajectory sidecars

[mjacobs]

Adds support for <uuid>.trajectory.json sidecars next to the existing AES-encrypted <uuid>.pb files under ~/.gemini/antigravity-cli/{conversations,implicit}/. The sidecars are produced out-of-process by agy-reader, which holds the decryption path and writes the resulting transcript as plain JSON; agentsview's parser now detects the sidecar and uses it as the source of truth for messages, tool calls, and tool results, falling back to the existing history.jsonl + brain artifact path when no sidecar is present. The sync engine treats the sidecar as part of the session for change detection (combined mtime/size via AntigravityCLIFileInfo) and forces message replacement on AgentAntigravityCLI sessions so trajectory updates land cleanly. Per the trust-boundary table in SECURITY.md, sidecars are treated as untrusted structured input under the "Imports and new readers" row: the parser is defensive against unknown step types, volatile fields are decoded through json.RawMessage accessors, and reads are size-capped at 64 MB. No new outbound channel is introduced; agy-reader is local-only. The legacy in-process ANTIGRAVITY_KEY decrypt path is preserved as a fallback for users without agy-reader installed; consolidating on the sidecar path is left for a follow-up.

[roborev-ci]

roborev: Combined Review (8a63e5c)

High severity issue found: incremental Antigravity CLI sync can miss sidecar-only updates.

High

• internal/sync/engine.go:2180
  • discoveredFileMtime still uses the main .pb file mtime for parser.AgentAntigravityCLI sessions. If only the .trajectory.json sidecar changes, SyncAllSince can filter the session out before processFile uses AntigravityCLIFileInfo, so polling/incremental sync misses transcript updates until a full sync or direct file event.
  • Fix: add an AgentAntigravityCLI branch that returns parser.AntigravityCLIFileInfo(file.Path).ModTime().UnixNano(), plus a regression test for sidecar-only updates.

Medium

• internal/parser/antigravity_cli.go
  • In flushPendingResults inside parseAntigravityCLITrajectory, pendingResultsTime is not reset after flushing. Later tool result messages can inherit the previous result timestamp, causing incorrect ordering or timestamps in the UI.
  • Fix: reset pendingResultsTime = time.Time{} after appending the flushed message and clearing pendingResults.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)

[roborev-ci]

roborev: Combined Review (3a4fe48)

Medium issue found; no Critical or High findings.

Medium

• internal/parser/antigravity_cli.go:148
  A syntactically valid but unusable sidecar, such as {} or one containing only unknown step types after schema drift, sets hasTrajectory = true and suppresses the history/decryption fallback. Because Antigravity CLI sessions are now force-replaced during sync, this can replace existing summary-mode messages with an empty session.

  Suggested fix: Treat a trajectory as present only after decoding at least one supported/displayable message, or make zero supported steps return an error so the existing fallback path runs. Add a regression test for {} or unknown-step sidecars.

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Synthesized from 3 reviews (agents: codex, gemini | types: default, security)

[mariusvniekerk]

This helps maintain feature compatibility with the older gemini cli, thanks a lot for this one