feat: add DeepSeek chat-template routing probe

experiments/deepseek/README.md

@@ -153,3 +153,55 @@ python -B experiments/deepseek/compare_routing_length_control.py \
 See `research/DEEPSEEK_ROUTING_LENGTH_CONTROL_AUDIT.md` for the sampling bias
 audit, paired CV/JSD deltas, total-variation accounting, and interpretation
 boundaries.
+
+## Official chat-template sensitivity
+
+`v2_lite_routing_template_probe.py` renders three variants of one fixed
+23-content-token prefix:
+
+```text
+raw         BOS + content
+user        BOS + "User: " + content + "\n\n"
+generation  user prefix + "Assistant:"
+```
+
+The latter two use the pinned official `chat_template` through
+`apply_chat_template`. All three variants of one source prompt execute in the
+same padded batch. Statistics are split between:
+
+- the full operational input, including wrapper tokens;
+- the exact intersection of `(relative character span, token ID)` inside the
+  source content across all three variants.
+
+The `user → generation` comparison is a causal negative control: the appended
+suffix must not change routes on their shared prefix.
+
+```bash
+PYTHONPATH=/path/to/transformers-4.41.2-deps:/usr/lib/python3/dist-packages \
+python -B experiments/deepseek/v2_lite_routing_template_probe.py \
+  --artifact-dir /path/to/deepseek-v2-lite \
+  --human-eval /path/to/HumanEval.jsonl.gz \
+  --gsm8k /path/to/gsm8k/test.jsonl \
+  --tnews /path/to/tnews/test.json \
+  --tnews-archive /path/to/tnews_public.zip \
+  --wikitext /path/to/wikitext-validation.parquet \
+  --output src/data/deepseek-v2-lite-routing-template.json \
+  --per-domain 32 \
+  --content-tokens 23 \
+  --batch-prompts 8 \
+  --layers 7 \
+  --bootstrap 2000 \
+  --seed 20260729 \
+  --captured-at 2026-07-29T08:30:00+00:00
+```
+
+The three variants add 382,032 real top-6 route selections. Across six MoE
+layers, all 21,852 `user → generation` shared-prefix token routes are
+ordered-top-6 exact. The committed run and independent rerun are byte-exact:
+
+```text
+da1f10333b2fa269e64f9716a0ca6c1a656d23d3e70b8a25d6e59f8a5b3bc1b9
+```
+
+See `research/DEEPSEEK_ROUTING_TEMPLATE_AUDIT.md` for the aligned-content
+contract, paired intervals, per-token route stability, and claim boundaries.