feat(hotpath): fill lcm schema/gc/describe gaps

[ScriptedAlchemy]

Summary

Fills the remaining hotpath coverage gaps in crates/tracedecay-lcm only (HP-lcm). Adds 25 #[hotpath::measure] attributes across the previously uninstrumented files — 21 async spans (future = true) plus 4 sync filesystem/CPU spans. No other crates touched, no Cargo.toml changes, no tokio_runtime! introduced, and hotpath stays opt-in (attributes are no-ops without the hotpath feature, exactly like the crate's existing instrumentation).

Labels follow the crate's established sessions.lcm.<area>.<verb> convention so new spans group with the existing ones (e.g. alongside sessions.lcm.gc.preview / sessions.lcm.gc.apply); the user-specified lcm.<area>.<verb> shape is preserved as the meaningful suffix.

Instrumented functions

schema.rs — require_admissible_lcm_schema (schema.admit), ensure_lcm_schema_in_transaction (schema.ensure — the production schema owner; ensure_lcm_schema itself is #[cfg(test)]-only and skipped per the no-tests rule), raw_fts_structure_is_current (schema.verify_raw_fts), rebuild_raw_fts (schema.rebuild_raw_fts), load_raw_message (raw.load_message).

query/describe.rs — raw_message_overviews, summary_overviews, describe_summary_node, describe_summary_sources, describe_external_payload under sessions.lcm.describe.*.

gc/pending_delete.rs — stage_payload_delete (gc.stage_delete), drain_pending_payload_deletes_matching (gc.drain_pending_deletes — single measure point shared by both public drain wrappers), probe_metadata_rows (gc.probe_pending_metadata).

gc/placeholder_scan.rs — scan_placeholder_text_rows (gc.placeholder_scan), any_placeholder_text_row (gc.placeholder_probe), count_placeholder_text_rows (gc.placeholder_count).

gc/orphan_scan.rs — preview_orphan_files (gc.orphan_preview, sync fs scan), stage_orphan_files (gc.orphan_stage).

payload/delete_recovery.rs — delete_external_payload_in_transaction (payload.delete), prepare_external_payload_delete_in_transaction_with_cache (payload.delete_prepare), tombstone_residual_placeholders (payload.tombstone_placeholders), plus sync fs spans remove_committed_payload_file_with (payload.remove_file) and payload_file_fingerprint (payload.fingerprint).

maintenance.rs — backup_database (maintenance.backup), payload_metadata_refs (maintenance.scan_payload_refs — shared by both public ref-collection wrappers).

Skipped per instructions: tests/#[cfg(test)] helpers, trivial single-row accessors (get_gc_meta/set_gc_meta/clear_gc_meta, schema_version), and private probes already covered by their instrumented callers.

Verification

• cargo check -p tracedecay-lcm (default features): pass
• cargo check -p tracedecay-lcm --features hotpath: pass
• cargo clippy -p tracedecay-lcm --all-targets --features hotpath: clean (one pre-existing warning in untouched tracedecay-graph-db)
• cargo test -p tracedecay-lcm: 162 passed, 0 failed, 1 ignored across 5 suites

  

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[github-actions]

Performance Comparison codex/tracedecay-total-redesign-plan-reopened → cursor/hotpath-lcm-gaps-710c

Total Elapsed Time: 5.40s → 5.03s (-7.0%)
CPU Baseline: 90.36µs → 90.39µs (+0.0%)
Benchmark ID: index-bench-timing

timing - Execution duration of functions.

+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| Function                                 | Calls                      | Avg                            | P95                            | Total                            | % Total                      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| tracedecay-index-bench                   | 1 → 1 (+0.0%)              | 5.40s → 5.03s (-6.9%)          | 5.41s → 5.03s (-7.0%)          | 5.40s → 5.03s (-6.9%)            | 100.00% → 100.00% (+0.0%)    |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.append_pages              | 13 → 13 (+0.0%)            | 194.77ms → 178.15ms (-8.5%)    | 268.70ms → 242.75ms (-9.7%)    | 2.53s → 2.32s (-8.3%)            | 46.86% → 46.08% (-1.7%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.batch.sqlite              | 13 → 13 (+0.0%)            | 123.47ms → 121.46ms (-1.6%)    | 167.38ms → 165.54ms (-1.1%)    | 1.61s → 1.58s (-1.9%)            | 29.71% → 31.42% (+5.8%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.batch.postings            | 13 → 13 (+0.0%)            | 108.24ms → 106.50ms (-1.6%)    | 147.19ms → 146.01ms (-0.8%)    | 1.41s → 1.38s (-2.1%)            | 26.04% → 27.55% (+5.8%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.workers.install               | 83 → 83 (+0.0%)            | 18.37ms → 15.10ms (-17.8%)     | 73.53ms → 50.99ms (-30.7%) 🚀  | 1.53s → 1.25s (-18.3%)           | 28.23% → 24.93% (-11.7%)     |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| CodeIndexProductionOwnerV1::extract_file | 276 → 276 (+0.0%)          | 4.45ms → 4.51ms (+1.3%)        | 6.86ms → 6.82ms (-0.6%)        | 1.23s → 1.25s (+1.6%)            | 22.76% → 24.78% (+8.9%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.build.and_publish             | 2 → 2 (+0.0%)              | 514.85ms → 506.25ms (-1.7%)    | 521.93ms → 508.30ms (-2.6%)    | 1.03s → 1.01s (-1.9%)            | 19.06% → 20.15% (+5.7%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| domain.canonical.sha256                  | 114526 → 114526 (+0.0%)    | 8.73µs → 8.56µs (-1.9%)        | 13.98µs → 13.91µs (-0.5%)      | 999.46ms → 980.32ms (-1.9%)      | 18.50% → 19.50% (+5.4%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.finalization.advance_wake | 14 → 14 (+0.0%)            | 55.58ms → 52.98ms (-4.7%)      | 275.78ms → 266.60ms (-3.3%)    | 778.17ms → 741.71ms (-4.7%)      | 14.40% → 14.76% (+2.5%)      |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.prepare_pages             | 13 → 13 (+0.0%)            | 60.88ms → 46.96ms (-22.9%) 🚀  | 89.19ms → 68.09ms (-23.7%) 🚀  | 791.46ms → 610.45ms (-22.9%) 🚀  | 14.65% → 12.15% (-17.1%)     |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.chunk.index_file              | 276 → 276 (+0.0%)          | 2.05ms → 2.10ms (+2.4%)        | 3.05ms → 3.09ms (+1.3%)        | 564.57ms → 579.99ms (+2.7%)      | 10.45% → 11.54% (+10.4%)     |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.extract.parser_artifact       | 276 → 276 (+0.0%)          | 1.89ms → 1.89ms (+0.0%)        | 2.90ms → 2.84ms (-2.1%)        | 520.56ms → 521.41ms (+0.2%)      | 9.63% → 10.37% (+7.7%)       |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| query.artifact.batch.parallel_prepare    | 13 → 13 (+0.0%)            | 49.94ms → 36.49ms (-26.9%) 🚀  | 73.73ms → 52.89ms (-28.3%) 🚀  | 649.18ms → 474.32ms (-26.9%) 🚀  | 12.02% → 9.44% (-21.5%) 🚀   |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.build.assemble                | 2 → 2 (+0.0%)              | 189.33ms → 186.55ms (-1.5%)    | 202.51ms → 196.21ms (-3.1%)    | 378.66ms → 373.10ms (-1.5%)      | 7.01% → 7.42% (+5.8%)        |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+
| code_index.chunk.build                   | 276 → 276 (+0.0%)          | 1.25ms → 1.26ms (+0.8%)        | 1.83ms → 1.81ms (-1.1%)        | 343.70ms → 347.48ms (+1.1%)      | 6.36% → 6.91% (+8.6%)        |
+------------------------------------------+----------------------------+--------------------------------+--------------------------------+----------------------------------+------------------------------+

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