# Design: Feedback Loop UX

## Summary

One new file (`db/feedback.rs`) with `FeedbackAction` enum, `FeedbackState` struct, `submit_feedback()`, `feedback_state()`, and `try_negative_preference_update()`. Two new methods on `UserStateIndex` (`remove_like`, `remove_save`). One new field on `TidalDb` (`skip_counter`). Re-exports in `lib.rs`. No WAL format changes. No schema changes. No new dependencies.

## Module Change Map

```
db/
  feedback.rs       <- NEW: FeedbackAction, FeedbackState, submit_feedback(), feedback_state()
  mod.rs            <- skip_counter field on TidalDb, pub mod feedback declaration
  from_parts.rs     <- skip_counter initialization in from_parts()

entities/
  user_state.rs     <- add remove_like(), remove_save() methods

lib.rs              <- pub use FeedbackAction, FeedbackState
```

## Data Structures

### FeedbackAction Enum (Copy, 11 variants)

All variants are data-free or contain only `u64`, making the enum `Copy`-able. Passed by value to `submit_feedback`.

### FeedbackState Struct (5 bools)

Read-only state derived from in-memory indexes. No I/O. `#[allow(clippy::struct_excessive_bools)]` applied since these are genuine independent boolean states for UI toggle rendering.

### Skip Escalation Counter

`skip_counter: DashMap<(u64, u32), u8>` on TidalDb. Incremented on each `NotInterested` action. At threshold (3), promotes to hard negative. Ephemeral (resets on restart).

## Method Implementations

### submit_feedback Dispatch

```
submit_feedback(user_id, entity_id, action, timestamp)
  |-- require_writeable("submit_feedback")
  |-- match action:
  |   Like:           signal("like") + add_like + mark_seen + try_update_preference_vector
  |   Unlike:         remove_like
  |   Hide:           signal("hide") + hard_neg.add + add_hide + mark_seen
  |   Unhide:         signal("hide", -1.0) + hard_neg.remove + remove_hide
  |   MuteCreator:    signal("block") + add_block_creator
  |   UnmuteCreator:  remove_block_creator
  |   Dislike:        signal("dislike") + hard_neg.add + mark_seen + try_negative_preference_update(0.3)
  |   UndoDislike:    hard_neg.remove
  |   Save:           add_save
  |   Unsave:         remove_save
  |   NotInterested:  signal("skip") + mark_seen + try_negative_preference_update(0.1) + skip escalation
  |-- Ok(())
```

### feedback_state Implementation

Reads from `user_state` and `hard_negatives` indexes. Distinguishes Hide (hidden_items + hard_neg) from Dislike (hard_neg only) by checking `hidden_items` bitmap presence.

### try_negative_preference_update

Reads item embedding, negates it, blends with reduced learning rate via `PreferenceVectors::update_with_custom_rate`. Uses `let...else` patterns for early returns on missing storage/embedding.

## Immediate Reflection Guarantee

DashMap insertions on the write side complete before `submit_feedback` returns `Ok(())`. DashMap reads on the query side in Stage 2.5 see the latest values. No cache, no eventual consistency, no batch buffer between write and read within the same process.

## Performance Characteristics

| Operation | Cost |
|-----------|------|
| `submit_feedback` (Like) | 1 signal write (~2us) + 2 DashMap inserts (~100ns each) + preference lookup (~500ns) |
| `submit_feedback` (Unlike) | 1 DashMap removal (~100ns) |
| `feedback_state` | 4 DashMap reads (~400ns total, no I/O) |
| Skip escalation check | 1 DashMap entry + u8 compare (~100ns) |