feat: action tagging in distillation for implicit behavioral pattern detection

[BYK]

Summary

Adds behavioral action tags to the distillation observer prompt and mechanical cross-session counting to detect implicit user preferences.

Eval Results

PR-2 (implicit preferences): 3.50 → 4.58 (tail-window: ~4.85)

Question	Before	After
Tests alongside implementation	1.4	3.6
Error handling in API endpoints	3.0	4.2
After implementing, what next	2.0	5.0
Route handler error pattern	2.0	4.2
const vs let	5	5
ORM stance	5	4.6
ORM for queries	5	5
const for vars	5	5

How it works

Action tags in distillation

The distillation observer prompt now tags user behavioral actions with bracketed labels:

🔴 [requested-tests] User asked for tests after implementing the POST /users endpoint
🔴 [corrected-style] User corrected let to const for non-reassigned variable
🔴 [rejected-approach] User rejected ORM suggestion, prefers raw SQL

Tags use a consistent [verb-noun] format so the same behavior in different contexts (testing REST endpoints vs React components) gets the same tag.

Cross-session counting

After each distillation segment, action tags are extracted via regex and counted across distinct sessions in the project. When a tag appears in 3+ sessions, a preference entry is auto-created at confidence 0.8.

Why this works where embeddings didn't

Vector similarity compares surface text — 'write tests for REST endpoints' and 'add tests for React components' are topically different. Action tags abstract the behavior into a canonical label ([requested-tests]), making the pattern countable regardless of context.

Files Changed

• packages/core/src/prompt.ts — BEHAVIORAL ACTION TAGS section in distillation prompt
• packages/core/src/pattern-extract.ts — extractActionTags(), tagToTitle()
• packages/core/src/distillation.ts — tag counting + preference creation after distillation