## What
- publishes Plan v2 content-addressed artifacts directly from the Cloud Run planner's private staging directory to GCS
- commits the Plan v2 manifest only after every referenced artifact is durable
- removes the second local Plan v2 CAS directory and preserves the existing Cloud Workflows wire contract
- exports a reusable GCS publisher adapter
## Why
Cloud Run planner, chunk, and assembler requests are independent containers and do not share a filesystem. The distributed contract must contain only durable GCS locators.
This layer makes the Plan v2 publication path object-store-native. Like the AWS parent PR, it still relies on one planner-local frozen v1 tree inside the producer; eliminating that remaining staging tree requires direct Plan v2 emission in a later layer.
## Design invariants
- local paths never cross a request or worker boundary
- manifest and artifact locators derive from one validated GCS output prefix
- immutable objects use generation-zero conditional creation and exact digest/size verification
- retries may reuse exact objects but never overwrite conflicts
- the manifest is the final publication commit point
- chunk and assembler requests independently download and verify only their target artifacts
## Test plan
- [x] all 95 GCP Cloud Run package tests pass
- [x] package typecheck passes
- [x] package build passes
- [x] changed-file lint, format, fallow, and repository commit gates pass
- [x] end-to-end adapter test covers plan, target-scoped chunk, and assemble through Fake GCS with no shared local directory
R3 review follow-ups on the keyframe cache:
- clearKeyframeCacheForFile collected ids from the index.html alias prefix
too, so a re-scan of one composition file wiped rows a sibling file had
just written (several files re-scan concurrently). Only the file's own
prefixed keys name the ids now; clearKeyframeCacheForElement still takes
the alias and bare key with them.
- toClipKeyframes fell back to a fixed 1s tween duration, which put a
duration-less tween's keyframes at a percentage no edit path agreed with.
It now spans the clip, matching resolveEditableTweenDuration.
- collectAnimatableKeyframeProperties takes `object` so call sites drop
their `as Record<string, unknown>` casts.
Regression tests cover both fixes.
Each keyframe-cache writer re-derived a clip-relative percentage inline, and the
post-commit writer rounded to 0.1% while the others used 0.001%. Selection keys
embed that number, so a commit-time rewrite could orphan a live key.
toClipPercentage owns the rounding, toClipKeyframes owns the whole row (percentage
plus the tween percentage and animation identity the lanes read), and the parsed
write reuses elementCacheKeys instead of open-coding the three key variants.
James Russo