…(F-DISTILL-SHARD-BATCH-001/002)

Closes the cross-component contract gap that the Blackwell cascade
post-mortem (lesson #2) identified: cache machinery is silent on
divergences between producer and consumer, until live dispatch
surfaces the failure. Same risk class for ShardBatchSource: its
wrap-around / cursor / chunk semantics need fixture-driven verification.

Adds two tests gated on `shard-batch-source` feature:

  F-DISTILL-SHARD-BATCH-001 — happy path
    Writes a tiny .bin shard with [0, 1, ..., 4095] tokens, opens via
    ShardBatchSource::from_dir, asserts:
      - batch shape (4 rows × 16 tokens)
      - all returned tokens lie in [0, 4096) (fixture range)
      - labels in same range
    Catches: any cursor-off-by-one or layout swap that produces
    garbage outside the fixture range.

  F-DISTILL-SHARD-BATCH-002 — wrap-around
    Writes only 128 tokens (enough for ~1.88 batches at bs=4, seq=16),
    consumes 5 batches in a row. Asserts no error — wrap_around=true is
    the default for ShardBatchSource. Catches: regression where the
    iterator returns None on exhaustion despite the constructor
    setting wrap_around.

Test plan:
- [x] 63 distill lib tests pass (was 61; 2 new)
- [x] `cargo test --features shard-batch-source` clean

These two tests would have caught most ShardBatchSource bugs at PR-time
instead of at gx10-dispatch-time, where each failure costs 5-15min.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

…ischarged; supersedes #1843) (#1844)

* spec: qwen3-moe-repetition-penalty-v1 — third 3-knob follow-up to M32d

Registers a new provable contract for repetition penalty
(`repeat_penalty` + `repeat_last_n`) on the qwen3_moe inference path.
Completes the 3-knob toolkit alongside:

- qwen3-moe-sampling-v1 (#1837 contract + #1842 impl) — temperature/top_k/top_p
- qwen3-moe-streaming-sse-v1 (#1835) — per-token SSE streaming
- qwen3-moe-repetition-penalty-v1 (this PR) — repeat_penalty / repeat_last_n

## Motivation

`QuantizedGenerateConfig` has `repeat_penalty` (f32) + `repeat_last_n`
(usize) fields. The dense path's `sample_advanced` applies them. The
qwen3_moe path's new `sample_from_logits` (added by #1842) does NOT.

Empirical observation from M287 evidence: Qwen3-Coder-30B-A3B is
generating REPEATED restatements in its turn-1 output (same Rust
snippet 3× in fixture leetcode__01-two-sum). Repetition penalty
(typically 1.1-1.3) would down-weight recently-generated tokens,
breaking the textual loop and forcing the model to either commit to
a tool call or change tactics.

## Falsification gates

- V1_001: `repeat_penalty == 1.0` is a no-op (backwards compat)
- V1_002: `repeat_penalty > 1.0` down-weights repeated tokens
- V1_003: `repeat_last_n` bounds the window correctly
- V1_004: companion-side bench with penalty produces a measurably
  different outcome distribution than the greedy baseline

## Implementation phases (engineer playbook)

- Phase 1 (~1hr): extend `sample_from_logits` signature with
  `recent_tokens: &[u32]` parameter; apply penalty as Step 1
- Phase 2 (~30min): plumb `&tokens` through decode loop
- Phase 3 (~2hr): unit tests + companion-side bench env-var plumbing

Total ~3-4 hours; operator-actionable any time post-M32d-merge.

## NOT in scope

- Mirostat / DRY / other penalty schemes
- Per-token logit biases
- Dynamic per-position penalty
- Companion-side bench env-var plumbing (separate companion PR;
  this contract is aprender-side only)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* feat: qwen3-moe-repetition-penalty-v1 implementation (V1_001-V1_003 discharged)

Implements the qwen3-moe-repetition-penalty-v1 contract. Bumps the
contract v1.0.0 → v1.1.0 with status_history. Supersedes #1843
(which was contract-only).

## Implementation

`crates/aprender-serve/src/infer/qwen3_moe_generate.rs`:

- `sample_from_logits` signature extended with `recent_tokens: &[u32]`
  parameter
- Repetition penalty applied as **Step 1** (BEFORE temperature scaling)
- Mirrors Candle's `apply_repeat_penalty` semantics (PMAT-383/384,
  dense path's `sample_advanced` in `gguf/inference/fails.rs:100`):
  - For positive logits: `logits[idx] /= repeat_penalty`
  - For negative logits: `logits[idx] *= repeat_penalty`
- Window: last `repeat_last_n` tokens from `recent_tokens`
- No-op when `repeat_penalty == 1.0` OR `repeat_last_n == 0`
- Decode loop passes `&tokens` slice (cheap borrow; no allocation per token)

## Test results

12/12 tests pass in `cargo test sample_from_logits_tests`:

- 4 original sampling tests (V1_001 greedy fallback, V1_002 seeded RNG,
  V1_003 seed divergence, V1_004 top_k=1 forces greedy)
- 5 NEW rep-penalty tests:
  - V1_001a: repeat_penalty=1.0 no-op
  - V1_001b: repeat_last_n=0 no-op
  - V1_002a: positive-logit branch (division)
  - V1_002b: negative-logit branch (multiplication; Candle convention)
  - V1_003: repeat_last_n window bounds (n=0/n=2/n=8 different effects)
- 3 edge cases (empty logits error, top_p=1 no-op, signature
  compatibility)

## V1_004 (operator-coordinated bench discharge)

Operator can dispatch companion-side bench with
APR_AGENT_REPEAT_PENALTY=1.2 + APR_AGENT_REPEAT_LAST_N=64 once
companion-side env-var plumbing (Phase 3 of #1843) lands. Bench
script + analyzer already pass through `gen_config` to
`run_qwen3_moe_generate` — this PR makes that pass-through actually
apply repetition penalty.

## Stacked on

#1842 (qwen3-moe-sampling-v1 implementation; the
`sample_from_logits` helper this PR extends).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>