lab: technique-aware fingering, oracle stage — does hand attribution explain the tapping slice?

docs/decisions.log.md

@@ -2954,3 +2954,22 @@ Architectural decisions go to [`adr/`](adr/) instead.
   tuplet import fix #202). The discriminating
   information is contextual, so the next Lab subject (chord voicing) is also
   what makes such anchors available for MIDI-sourced material.
+
+- 2026-09-17 — In the context of the fingering objective failing completely
+  on lines with tapped notes (no human path in the model's optimum set), we
+  decided to **test hand attribution as an oracle first — tap labels from
+  the tab, same weights, exact DPs — before any hidden technique
+  inference**, to achieve a clean attribution of that failure, accepting
+  that the result says nothing yet about MIDI-sourced material. Result
+  (`docs/audit/2026-09-fingering-tap-attribution.md`): attribution brings
+  the tapped slice to parity with length-matched untapped lines on excess
+  per note (2.94 → 1.27 vs 1.26), agreement (39.4% → 44.3% vs 44.9%) and
+  ceiling, but not on exactness (1.3% vs 21.0% of lines with the human path
+  in the optimum set). Under the current objective's decomposition, 75% of
+  the residual cost falls on the fretting-hand travel term; with tapping
+  figures seemingly kept on one string, legato continuity is the hypothesis
+  to test next, as an observed-label oracle before technique inference.
+  (Revised after the import fixes #201 and #202: GP6/7 tapping now reaches
+  the slice (226 lines). Attribution closes most, not all, of the excess gap
+  (3.20 → 1.63 against 1.16, 77%). Exactness stays out of reach, 0.9% against
+  20.0% — see the audit's re-measurements.)

lab/README.md

@@ -107,6 +107,17 @@ with and without the line's hand anchor.
 
 Results: [`../docs/audit/2026-09-fingering-tie-break.md`](../docs/audit/2026-09-fingering-tie-break.md).
 
+## Technique-aware fingering (oracle stage)
+
+`src/technique.rs` attributes tapped notes (`TabLine::tapped`, from the tab)
+to the picking hand: the fretting hand's anchor carries across taps, and the
+picking hand pays its own travel. `tap_aware_chain` encodes it for the exact
+optimum-set DPs. `fingering_gap taps` compares tap-blind and tap-aware models
+under the same weights on lines with tapped notes, with an untapped baseline
+reweighted to the same line lengths.
+
+Results: [`../docs/audit/2026-09-fingering-tap-attribution.md`](../docs/audit/2026-09-fingering-tap-attribution.md).
+
 ## Known spike limits (deliberate)
 
 - The reference solver is leaf-checked backtracking with two sound band