Index values in variable-arity sequence tables

[ezrosent]

Summary

• Add an optional occurrence index mapping selected semantic values to the sequence rows containing them.
• Allow encodings to exclude headers, masks, and metadata through a configurable value visitor.
• Support candidate-only indexed rebuilds and refresh the index across appends, deletes, and compaction.
• Cover selected-position indexing, parallel compaction, and sparse rebuilds.

Stack

Draft, stacked on #974. This is PR 2 of 12 in the sequence-backed container stack.

Validation

Validated on the complete 12-commit stack:

• cargo nextest run --workspace: 1,362 tests passed
• cargo test --workspace --doc
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.68750% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.64%. Comparing base (1b22eca) to head (c6a903a).

Files with missing lines	Patch %	Lines
core-relations/src/table/sequence.rs	90.00%	27 Missing ⚠️
core-relations/src/hash_index/mod.rs	88.00%	6 Missing ⚠️

Additional details and impacted files

@@                              Coverage Diff                              @@
##           codex/inline-containers-01-sequence-table     #975      +/-   ##
=============================================================================
+ Coverage                                      87.56%   87.64%   +0.08%     
=============================================================================
  Files                                             97       97              
  Lines                                          36183    36491     +308     
=============================================================================
+ Hits                                           31683    31982     +299     
- Misses                                          4500     4509       +9     

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[codspeed-hq]

Merging this PR will degrade performance by 7.25%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 35 untouched benchmarks
⏩ 227 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	tests[eggcc-2mm]	7.9 s	8.7 s	-9.42%
❌	Simulation	rust_rule_match_overhead[rule_run_1]	13.8 ms	14.6 ms	-5.03%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing codex/inline-containers-02-sequence-indexes (c6a903a) with codex/inline-containers-01-sequence-table (1b22eca)}

Footnotes

1. 227 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩