fix(branches): use unique table forks and defer reclamation to cleanup

[azimafroozeh]

What & why

After a fast-forward leaves a child using an owner's earlier table fork, the owner can refuse its next write because the fixed fork name is still occupied. Give each first-touch attempt a bounded, unique fork name and persist it through the existing recovery intent, so subsequent writes preserve the child's snapshot.

Only explicit cleanup reclaims table forks. Parent deletion records logical retirement in native ref metadata and retains the ancestry needed by descendants. Eligible branch-source fast-forwards adopt table pointers while preserving constraint checks and later write isolation.

Backing issue / RFC

• Implements and amends accepted RFC 0042.
• Regression coverage extends the scenario from issue 683.

Checklist

• Change is focused (one logical change).
• Tests added or updated for behavior changes.
• Public and developer documentation updated.
• Reviewed against architectural invariants.

Local verification

• cargo test --workspace --locked --offline --features omnigraph-engine/failpoints,omnigraph-cluster/failpoints --no-fail-fast: 3,256 passed, 24 ignored, zero failures.
• From crates/omnigraph-dst, cargo test --profile dst --locked --offline -p omnigraph-dst --no-fail-fast: 78 passed, 31 ignored, zero failures. The cost golden replays identically.
• cargo clippy --workspace --all-targets --locked --offline -- -D warnings -W clippy::dbg_macro: passed.
• cargo clippy --workspace --all-targets --locked --offline --features omnigraph-engine/failpoints,omnigraph-cluster/failpoints -- -D warnings -W clippy::dbg_macro: passed.
• cargo fmt --all --check, documentation, comment, agent-index, workflow-pin, typo and diff checks: passed.

S3/Azure environments and predecessor binaries were not configured locally. CI results are pending.

Notes for reviewers

The internal schema advances to v8 because older engines do not understand retired native refs. The compatibility tests cover refusal and rebuild rather than opening v8 data with an older engine.

The dependency remains unmodified registry Lance 11.0.0. An engine-owned CommitHandler preserves inherited index origins in the existing clone publication, including fragment-reuse details. Nested BTREE, full-text and vector reads are tested through cold reopen. Indexed clone preparation adds metadata reads; ordinary non-clone commits forward without adapter I/O.

Retained physical refs can increase cold logical-resolution reads. Native branch retirement retains the existing single-writer-process boundary. Cleanup preserves required ancestors and applies the requested age limit before reclaiming unused forks.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-09T22:03:46.901733Z	b12d740	PR opened

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: b12d7408ae

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".