diff --git a/stacks/gemma4-charrp/compose.yaml b/stacks/gemma4-charrp/compose.yaml
index 10f7071..e335b89 100644
--- a/stacks/gemma4-charrp/compose.yaml
+++ b/stacks/gemma4-charrp/compose.yaml
@@ -75,12 +75,29 @@ services:
       # `char-rp-reasoning` alias exercises.
       - --default-chat-template-kwargs
       - '{"enable_thinking": false}'
-      # ⚠ NO --chat-template. MeroMero pointed at a hand-patched jinja under
-      # meromero-v2-nvfp4-work/; that patch was cut against THAT checkpoint and
-      # does not describe this one. This model ships its own chat_template.jinja
-      # and vLLM picks it up. If thinking mode ever misbehaves, diff this
-      # model's template against the MeroMero patch before reaching for a
-      # copy — do not assume the patch transfers.
+      # TEMPLATE PINNED EXPLICITLY, AND IT IS A NO-OP FOR THE DEFAULT MODEL.
+      # The A4 build ships this exact file — verified byte-identical to upstream
+      # google/gemma-4-26B-A4B-it once trailing newlines are normalised (390 vs
+      # 389 lines, same hash) — so pinning it changes nothing about what is
+      # served and permanently removes a real class of bug.
+      #
+      # ⚠ WHY IT IS PINNED AT ALL: the A16 control build at
+      # /tank/aimodels/gemma4-26b-a4b-it-nvfp4a16 ships a STALE 266-line
+      # template. Upstream and A4 open the thinking path with
+      # `{%- set enable_thinking = enable_thinking | default(false) -%}`; the
+      # A16 one has no such set, and its tokenizer_config response_schema lacks
+      # the `thinking` property. Serving it with its own template would render a
+      # DIFFERENT PROMPT, turning a one-axis activation-precision control into a
+      # two-axis comparison — a result that would look like a finding.
+      # Safe to force across both builds because the tokenizers are identical:
+      # vocab 262,144 entries, added_tokens identical.
+      #
+      # ⚠ IF GEMMA4_MODEL EVER POINTS AT A DIFFERENT CHECKPOINT, THIS DEFAULT
+      # MUST MOVE WITH IT. A pinned template is only correct for the checkpoint
+      # it came from. That is the inverse of the mistake the outgoing MeroMero
+      # seat warned about, where a hand-patched template was assumed to transfer.
+      - --chat-template
+      - ${GEMMA4_CHAT_TEMPLATE:-/tank/aimodels/gemma4-26b-a4b-it-nvfp4/chat_template.jinja}
       - --max-model-len
       - "${GEMMA4_MAX_MODEL_LEN:-262144}"
       - --max-num-seqs