Adopt upstream orchestrator v2 in full #988

Owning issue for adopting T3 upstream de34391427, “feat(orchestrator): introduce new orchestrator (#2829)”, in full.

Implemented and merged: PR #989, merge commit 5f1af3418ed78fad5937450d54d2e62a2959253d, after merged prerequisite #987 (6f90102ce83f4599d7b07127ef59eb374ad845c9). All cherry-pick conflicts are resolved, v1 orchestration is deleted, and WIP history is replaced by seven per-area review commits. Production apps/server/src/orchestration-v2 is byte-for-byte upstream. Five test-only exceptions are authorized: Pylon migration numbering in LegacyV1Cutover and ProjectSettingsUpgrade, the resolved-target importer boundary required for Prime, and ACP/Codex Pylon branding expectations.

Prime is registered through the Pylon v1→v2 bridge. Native Prime rollback/fork/active steering, total-cost projection and automatic adoption of active execution across any server restart remain unsupported for this landing, including pre-cutover v1 authority; stop/drain Prime work before restarting or upgrading. Native queue, side-question, resource, goal/depth, direct child and compaction/harness controls are also unavailable; see the initial Prime limitations. Receipt-proven maintenance remains quarantined until cleanup, survives client disconnect and retries durable scheduled work at startup. The maintainer confirmed dropping durable rollback sagas and Codex absolute rollback in favor of v2 rollback. All keep/drop decisions and the bridge event map remain in the maintainer's local plan.

V2 writes userdata/statev2.sqlite; Pylon migrations 68/69 replace upstream55/56 and the unrelated preview reconciliation is removed. A read-only Nightly DB copy imported 307 threads and 48,062 messages, drained all pending hydration, and repeated without duplicates or changing the source copy. No live userdata was used as server/test state.

Validation: affected package direct typechecks, focused core/Prime/client/provider regressions, changed-scope formatting/lint and server bundles pass. A rebuilt native iOS development build passed; web/fresh simulator verification used a synthetic completed transcript, pairing and reversible settings without starting provider turns. Synthetic screenshots/video are uploaded on the PR. Independent final review fixes pass 87 Prime lifecycle and 376 web handoff/composer tests; both exact CI Knip commands pass. CI is green on final head 603f8ab3ba (full CI, mobile native analysis); all test shards, typechecks, lint, builds and packaged smoke checks pass. The maintainer approved landing on 2026-10-03; both PRs are merged. Pairing/cache also pass native/JS cold restart, offline fallback and automatic reconnect; no source fix was justified for an earlier non-reproducing cache warning. No release or installation was performed.

Mobile compatibility is confirmed at the wire: WS requires orchestrationProtocol=2 (old/missing→426); orchestration HTTP requires x-t3-orchestration-protocol:2; graph/snapshot/event/command shapes break v1 consumers. Native composer changes also require a rebuilt compatible binary. Pylon keeps version 1.0.1; pinned upstream config is 1.4.0, correcting the earlier 2.0.0 assumption. Default fingerprint includes the native module; preview:local's appVersion override needs an explicit runtime/version decision before delivery. No EAS, OTA, store release or device update is authorized/performed by this adoption.