Merge origin/master (generic task runtime #219, single-exe closure, package renames)

Semantic resolutions beyond line merges:
- The bash seam keeps resolveMode + the bash/resolve-mode waterfall on
  master's task-free BashExecutor (run/start/resolve only; BashProcess
  handles); tool-bash consults it at its stamping site and escalation
  baseline on master's render/background split, with a waterfall test on
  the recording executor.
- dsh-mode's BASH_FAMILY narrows to ['bash']: bash_output/bash_kill are
  replaced by the kind-generic task_output/task_kill, which span every
  task kind and only observe or stop work, so the access cap withholds
  only the starter it can reason about.
- The plan-mode snapshot suite adopts master's pin grammar (tool-schema
  sidecars; the expectedHeaderSnapshots extension is gone — the exit
  transition deltas, and entering-before-turn-1 needs no second
  snapshot); modes-advertise joins the plan header class (no-model, so
  membership is vacuous). Fixtures re-recorded on the acp-demo bin;
  the replay overlay gains the passthrough sandbox runner.
- examples/plan-acp-agent rewires to @deepseek-ai/dsh-acp-demo and drops
  its tool-bash entry (the spine bundle now composes it); dsh-stdio (the
  renamed stdio-chat home) keeps its /mode command and gains the dsh-mode
  peer edge; the acp bridge keeps the modes surface beside master's
  permission presets.
- mode README gains the Model Experience / Known Limitations sections the
  new README gates require; AGENTS.md ceiling 1370 → 1440 for the kept
  mode/ layout line and Agent efficiency section.

packages/llm/llm-deepseek/src/serialize.ts

@@ -1,17 +1,8 @@
 /**
- * Serialize harness vocabulary (`GenerateOptions`, `Message[]`) into the
- * DeepSeek chat-completions request body.
- *
- * Block-type mapping (core types handled explicitly; merge-extensible unions
- * mean plugin-added block types exist — they are skipped, never errors):
- *
- * - user `text` → string content (joined)
- * - assistant `text` → `content`; `reasoning` → `reasoning_content`, but
- *   ONLY on assistant messages that carry tool calls (the official passback
- *   rule for thinking mode — required there, ignored elsewhere, so we save
- *   the tokens elsewhere); `tool-call` → `tool_calls[]`
- * - `tool-result` → its own `{role: 'tool'}` message (text flattened)
- *
+ * Serialize harness messages into DeepSeek chat completions. User text is joined; assistant text
+ * becomes `content`, tool calls become `tool_calls`, and tool results become separate tool messages.
+ * Assistant reasoning is replayed as `reasoning_content` only on tool-call turns, as required by
+ * thinking-mode passback. Unknown declaration-merged block types are skipped rather than rejected.
  * @module dsh-llm-deepseek/serialize
  */