fix(deepseek): review fixes for the transcript reader — docker/remote gate, poll memo, honest pairing docs

Four review findings on the worker-transcript feature:

- Docker and remote-SSH dsh sessions now keep the pane segmenter: their
  transcripts live in the container's / remote host's own ~/.dsh, which
  the local reader can never see, so the transcript path returned
  'nothing said yet' forever and an agent polling such a worker starved
  on an answer that existed. Gated on !session.docker && !session.remote
  (statically pinned) and documented in the integration guide.

- last-response reads are memoized on (path, mtime, size, blocks): the
  skill's last_text polls once per second, and each poll decompressed and
  reparsed the whole file on the event loop even when nothing had been
  appended. An unchanged poll now costs one stat.

- The pairing ladder's comment claimed /new is served by step 2; in truth
  the boot-window transcript wins for as long as it exists (deliberately:
  preferring newest-eligible would hand a worker its busier sibling's
  reply). The comment now states the real tradeoff instead of the
  aspirational one. Same for decodeZstdFrames' 'skipped' wording — a
  corrupt frame truncates the decode there, which is the safe behavior.

- stripReasoningPrefix no longer runs on user prompt text, so a prompt
  containing a literal </think> renders whole in blocks view.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/routes/session-routes.ts

@@ -2051,7 +2051,14 @@ export function registerSessionRoutes(
     // reply reads as a reply. So an EMPTY transcript result still wins over the
     // pane — "nothing said yet" is the honest answer. Only `null`, meaning a
     // Node too old to decode zstd, falls through to the segmenter below.
-    if (session.mode === 'deepseek') {
+    // ⚠️ Local sessions only: a docker case's harness writes its transcript
+    // inside the CONTAINER's ~/.dsh (the workspace bind-mount does not cover
+    // it) and a remote-SSH case's lives on the remote host, so the local
+    // reader would scan a $DSH_HOME that can never hold this session's file
+    // and return "nothing said yet" forever — an agent polling that worker
+    // would starve on an answer that exists. Those configurations keep the
+    // pane segmenter below: coarse, but the real conversation.
+    if (session.mode === 'deepseek' && !session.docker && !session.remote) {
       const deepSeekQuery = req.query as { context?: string };
       const full = deepSeekQuery.context === 'full';
       const transcript = await readDeepSeekLastResponse(session, { blocks: full });