## Why
Image files can become unavailable between turns. Model requests should reflect their current availability while preserving the original references in saved history.
## What changed
- Add opt-in availability checks through `AttachmentStore::is_resolvable`, retaining references by default and on backend or access errors.
- Check distinct file IDs concurrently for each prepared request and replace confirmed-missing images with `[image unavailable]` in messages and tool outputs.
- Apply the same handling to compaction requests, with background image checks running outside the session lock without delaying foreground turn completion.
## Testing
Add unit tests and multi-turn scenarios covering placeholders, preserved history and annotations, concurrent deduplicated checks, backend errors, and nonblocking background compaction.
GitOrigin-RevId: ec98c7014c6e6b5063d87b943d2cd66a9ce7c1e3
## Why
Polling a failed background compaction consumes the closed oneshot receiver.
Keeping that receiver in session state can cause a later await to panic instead
of falling back to foreground compaction.
## What changed
Remove the receiver from session state before polling it, restoring it only when
its result is still pending. Discard closed receivers so compaction can fall back
normally.
## Testing
Add a regression scenario where background compaction fails before the next
checkpoint and automatic compaction falls back successfully.
GitOrigin-RevId: 1461bb403f4b0b8b7e171d1b3cba41411f2014b4
## What changed
- Launch background compaction at eligible pre-turn, mid-turn, and post-turn checkpoints when `AsyncCompaction` is enabled, capturing the current world state and client routing state.
- Adopt ready results at compaction checkpoints while preserving newer messages, tool outputs, and world-state updates. Continue normally if an optional result is rejected.
- Run one foreground compaction if an adopted result still exceeds the context limit.
- Prevent cancelled turns from launching new background work while preserving already-running work for later reuse.
## Testing
Add unit and scenario coverage for stale history and account changes, cancellation, pending-result reuse and fallback, retained tool outputs, compaction event pairing, and token usage accounting. Add a context snapshot covering a collaboration-mode change while compaction runs.
GitOrigin-RevId: 04ac028d9fe2e3ea64aacaaeb351c3c776cf3940
## What changed
- Await a compatible pending background request when foreground compaction is needed, and share the result installation path with foreground requests.
- Validate the captured history generation, prefix length, model, and authentication owner before installing a prepared result. Fall back to foreground compaction when required if the result is rejected.
- Replace only the captured history prefix, preserving later messages, retained tool outputs, goal edits, and the current world-state baseline. Record installation analytics and completion events only after a result is installed.
GitOrigin-RevId: 798963f2fc603c3febba2c21eafa1bcb094b3ebf
## What changed
- Capture history, prompt metadata, routing state, authentication ownership, and context-window identity for background compaction requests.
- Send background requests over HTTP while preserving foreground routing, and retain the latest candidate in session memory.
- Add feature and threshold eligibility checks and deduplicate attempts by history version, model, compaction hash, and authentication ownership.
- Cancel and drain background tasks during session shutdown, preserving completed usage accounting.
The background launch helper is not yet connected to the turn loop.
GitOrigin-RevId: 0e5e6ab7dac4d98a836733668a775ac48b5a59f1
Krish Chainani