fix(merge): a branch whose edits net to zero can never be merged

[ardacanuckan]

What & why

A branch whose edits return a table to its fork-point content could not be merged. The merge tried to publish a field-identical table registration, failed with a version collision, and failed the same way on every retry.

This fixes that path by planning adoption once and dropping a table candidate only when the planned registration is already the stored manifest row and the source and base rows are proven logically equal. The merge still publishes its graph lineage, while recovery intent, expected versions, and published table updates remain consistent.

The equality proof is deliberately typed rather than display-string based:

• non-Blob values use Arrow's null-aware logical equality;
• only the five exact Lance virtual columns are ignored, so legal fields such as _row_id remain visible;
• external Blob values compare their complete logical descriptor;
• managed Blob values compare descriptor plus normalized physical data-file identity, resolving inherited branch files through Lance base paths without reading payload bytes;
• Blob identity lookup is cached from active files, so work does not grow with retained branch ancestry.

The manifest publisher also accepts an idempotent re-registration of the exact stored row while continuing to reject a different row at an occupied identity/version.

Closes #473.

Recovery behavior

The crash test now pins the exact pre-confirmation outcome. Reopen rolls the unpublished sibling-table effect back, leaves the source delta available, and records one RolledBack audit entry. A clean retry must return Merged, publish the source and target rows together, and continue to suppress the net-zero table.

Coverage

• Net-zero merge shapes: fast-forward, diverged target, mixed tables, and branch-to-branch.
• Exhaustive merge truth table: 10×10 operations, 49 executable cells.
• Equality regressions: null vs empty string, delimiter collisions, legal _row_id, same-looking managed Blob descriptors from different files, and inherited managed Blob files across native branches.
• Existing Blob adopt path: one known-present update and no payload materialization for unchanged cells.
• Recovery failpoint: exact rollback state before retry and exact merged state afterward.

Local verification

• cargo test --workspace --locked --features omnigraph-engine/failpoints,omnigraph-cluster/failpoints
• cargo clippy --workspace --all-targets --locked -- -D warnings -W clippy::dbg_macro
• cargo clippy --workspace --all-targets --locked --features omnigraph-engine/failpoints,omnigraph-cluster/failpoints -- -D warnings -W clippy::dbg_macro
• cargo fmt --all --check
• scripts/check-agents-md.sh

Focused merge, Blob-adopt, truth-table, planner, and recovery tests also pass. The only local diagnostic was the existing macOS linker warning about compact-unwind metadata size.

Greptile Summary

The PR makes net-zero branch edits mergeable by removing manifest-identical adopt candidates before recovery and publication, while permitting idempotent manifest-row registration.

• Adds typed, physical-file-aware equality for Blob-bearing adopt scans.
• Introduces a pure three-state adopt publication plan shared by classification and publication.
• Expands net-zero, truth-table, publisher, and crash-recovery coverage.
• Documents the platform-specific stack requirement for the full test suite.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/omnigraph/src/exec/merge.rs	Replaces adopt signature comparison with typed equality and filters field-identical adopt plans before all candidate-derived recovery and publication state is built.
crates/omnigraph/src/blob.rs	Adds managed-Blob equality based on validated descriptors, row addresses, and resolved immutable data-file identity.
crates/omnigraph/src/db/manifest/publisher.rs	Allows idempotent re-registration of an identical stored version row while retaining rejection for differing occupied-version state.
crates/omnigraph/src/db/manifest/tests.rs	Distinguishes duplicate-request and stored-state collisions and covers both identical and differing re-registration behavior.
crates/omnigraph/tests/merge_net_zero.rs	Adds integration coverage for net-zero merges across fast-forward, divergent, mixed-table, and branch-to-branch shapes.
crates/omnigraph/tests/merge_truth_table.rs	Adds net-zero operations to the merge behavior matrix rather than treating them as manifest-equal no-ops.
crates/omnigraph/tests/failpoints.rs	Covers recovery after durable effects when a merge combines one net-zero table with a real delta.
docs/dev/testing.md	Documents the macOS test-stack requirement and its unrelated baseline behavior.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Compare base and source table rows] --> B{Validation delta empty?}
  B -->|No| C[Retain merge candidate]
  B -->|Yes| D[Plan adopted source state]
  D --> E{Planned registration}
  E -->|Nothing| F[Drop candidate before recovery planning]
  E -->|Pointer| C
  E -->|Fork| C
  C --> G[Build expected versions and recovery slots]
  G --> H[Publish table updates and graph head atomically]
  F --> G

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Context used (3)

• Knowledge Base — Branching and merge
• Knowledge Base — OmniGraph core storage: manifest, table store, and Lance access
• Knowledge Base — Dev conventions and invariants