[ragnorc]

RFC 0067 rollout step 4, second writer: ensure_indices and the explicit full-text rebuild stage detached commits. Stacked on #731 (mutation and load), which is stacked on #728, #727 and #725.

What changes

• Every index batch is a detached commit of the pinned base. maintain_indices_for_branch opens each productive table at its pin (open_pinned_for_write, promoting a pending predecessor first), stages the complete BTREE/FTS/vector batch before the gates as before, and under the gates commits each batch with commit_staged_detached, publishes the pins (expected + 1, staged, uuid) in the one manifest commit, and promotes them from the handles it holds. No EnsureIndices sidecar is armed, confirmed or deleted; the pre-minted transaction identities, the exact-commit outcome check and the RecoveryRequired wrapping are gone with it. A first-touch fork on a branch (explicit rebuild only) is created under the gates with no intent record, exactly like a mutation's first touch; its batch stages on the fork.
• The full-text certificate is unchanged: stage_create_indices writes it before the commit, the detached batch carries the same index uuid as its promoted twin, and search is served through a pending pin.
• Seams. ensure_indices.post_sidecar_pre_fork and ensure_indices.post_effects_pre_confirm are gone; ensure_indices.post_fork_pre_commit and ensure_indices.post_publish_pre_promotion are new; post_stage_pre_commit_btree, post_table_effect and post_phase_b_pre_manifest_commit keep their names over the detached effects.
• The classifier keeps the EnsureIndices sidecar kind for sidecars written before this change, as engine: mutation and load stage detached commits and publish pins (RFC 0067 step 4a) #731 did for Mutation/Load; step 5 removes them together. new_ensure_indices_sidecar_v9 is cfg(test), confirm_ensure_indices_sidecar_v9 is deleted.

Tests

• detached_commit_matrix.rs gains Writer::EnsureIndices (a declared BTREE the schema apply leaves unbuilt; the same windows, faults and recovery actors as an insert; the oracle additionally runs a converging index pass after recovery).
• failpoints.rs: the nine sidecar-era index tests (armed-effect rollback, partial arming, first-touch crash and rollback, post-effect winners, confirmed full-text recovery) retire with the sidecar; new ensure_indices_interrupted_after_publish_leaves_a_pending_pin_the_next_writer_promotes, ensure_indices_failure_before_publish_leaves_no_residue, full_text_rebuild_pending_pin_serves_search_and_promotes and full_text_rebuild_first_touch_fork_failure_leaves_no_residue. The recovery-machinery tests (discovery races, the cleanup barrier, the storage-fault contracts, in-process healing) now take their pending sidecar from branch merge (graph_with_merge_work + leave_confirmed_merge_sidecar); the schema-apply heal test produces its own schema-apply sidecar because schema apply needs a main-only graph. The blocked-pin test uses Optimize as the writer that still refuses.
• write_cost.rs: an index pass with work writes and deletes no control object.
• changes_cost.rs: the delta-bounded page cell seeds nine commits instead of eight so the padding dataset has rows at both depth points; the stale-index arm's index build then covers the same table set at both points. With the detached index build, a two-table index commit leaves the following page two __manifest fragment reads cheaper than a one-table one, which the old fixture (Company empty at the deep point only) read as growth with history; the page results and the deep point's cost are unchanged.
• The S3 sidecar-lifecycle cell from engine: mutation and load stage detached commits and publish pins (RFC 0067 step 4a) #731 takes its sidecar from branch merge, like the other machinery tests.
• crates/omnigraph-dst: the crash-window catalog follows the renamed index seams (the maintenance-obligation cell crashes the index writer at post_table_effect, the window that still leaves work), and the cost golden is regenerated for the index writer's detached batches.
• Docs: writes.md (writer table row and the index writer's protocol), recovery.md, testing.md, release note.

Notes

• Step 4 continues with branch merge, then schema apply, then Optimize.

[ragnorc]

Consolidated into #744, which carries this stack's complete history merged with current main and revalidated as one tree.