Taste/Style Profile Learning

Kerux learns portable, confidence-scored coding-style preferences from your trajectory history and injects them into the system prompt — so the agent writes code the way you do, across every project.

Inspired by CommandCode’s taste registry: preferences like export style: named exports (confidence 0.85) travel with the user, not the repo. Design reference: research/product-research-t_2be9e216.md (ide #9).

Data model

Everything lives in crates/kerux-core/src/taste.rs.

Supporting enums: PreferenceCategory (naming, formatting, architecture, tooling, language, documentation, testing, workflow, other) and PreferenceSource (extracted, inferred, manual).

Confidence scoring

Every preference counts supporting (positive) and contradicting (negative) observations. Confidence combines two factors (compute_confidence):

• Consistency — positive / (positive + negative). A preference that is contradicted half the time can never exceed 0.5.
• Saturation — n / (n + HALF_SATURATION) with HALF_SATURATION = 5. One observation yields ~0.17, five yield 0.5, twenty yield 0.8; confidence grows slowly and never quite reaches 1.0.

confidence = (positive / total) * (total / (total + 5))

No evidence scores 0.0 — nothing is injected until something is actually observed. The score is stored denormalized on the preference and recomputed whenever evidence changes (recompute_confidence); the raw counters are the source of truth.

Storage format

The portable JSON document is the profile itself (version field guards forward compatibility, missing fields get defaults so old documents stay readable):

{
  "version": 1,
  "name": "kerux",
  "created_at": 1787700000,
  "updated_at": 1787766000,
  "preferences": [
    {
      "key": "export style",
      "category": "language",
      "value": "named exports",
      "positive": 20,
      "negative": 1,
      "confidence": 0.8,
      "source": "extracted",
      "first_observed_at": 1787700000,
      "last_observed_at": 1787766000
    }
  ],
  "metadata": { "source_project": "kerux" }
}

Two locations, same format:

• Store (portable registry): FileTasteStore persists one pretty-JSON document per profile name under <data_root>/taste/<name>.json (~/.kerux/taste/, KERUX_HOME overrides the root). Names are sanitized for the filesystem.
• Project-local: <project_root>/.kerux/taste.json (project_taste_path) — commit it to version control to share a house style with your team via PR.

Writes are atomic (temp file + rename, via the shared persist helpers); missing or corrupt files read as “start fresh”.

Push/pull semantics

Push = load the project profile, save it into a TasteStore under a name. Pull = load from the store, TasteProfile::merge into the project profile. Merge rules, per matching key:

kerux taste push team
kerux taste pull team

Both commands use the current directory as the project root. Push requires an existing .kerux/taste.json; pull creates it when absent and atomically writes the merged profile.

• Same value: evidence counters add, the observation window widens (min first / max last), confidence recomputed.
• Conflicting values: the side with more total evidence wins (ties go to the more recently observed one).
• Manual source propagates: an explicitly stated preference (source: manual) wins over learned sources.
• Keys present on only one side are copied over; metadata keys missing from the target are filled in without overwriting.

Prompt injection

TasteProfile::render_prompt_block(min_confidence, max_items) renders the top preferences (highest confidence first, at most one entry per key, capped) as a markdown block:

## Learned Coding Style Preferences

Learned from past sessions. Follow these unless the user instructs otherwise.

- export style: named exports (confidence 0.80)
- naming: snake_case files (confidence 0.75)

Returns None when nothing clears the threshold or max_items == 0 — callers omit the block entirely rather than injecting an empty section. retain_confident(min) prunes weak preferences from a profile outright.

At runtime, [taste] enabled = true injects this block from the current project’s .kerux/taste.json. min_confidence defaults to 0.5 and max_items defaults to 10; setting enabled = false disables injection.

Extraction engine

crates/kerux-core/src/taste_extraction.rs implements PreferenceExtractor as TrajectoryPreferenceExtractor: a deterministic, LLM-free miner over recorded Trajectory steps (the canonical action record; messages mirror the same tool calls and are skipped to avoid double-counting). It emits supports = true evidence only — counter- evidence is reserved for explicit/manual signals.

Signals mined per trajectory step:

Retry-loop guard: identical (key, value) observations are capped per trajectory (max_repeats_per_trajectory, default 3), so one stuck session cannot saturate a preference. Confidence scoring stays in taste.rs — the extractor only emits evidence, folded via TasteProfile::apply_observations.

Division of labor

• taste.rs (this design): schema, scoring math, storage, merge, prompt rendering.
• taste_extraction.rs: TrajectoryPreferenceExtractor implements PreferenceExtractor; results fold via TasteProfile::apply_observations.
• System-prompt wiring and kerux taste push/pull CLI: built on TasteStore + render_prompt_block + project_taste_path.