feat(coding-agent): added todo batching guidance and armed prewalk when option is set

- Updated system and todo prompt templates to require batching todo tool calls with real action calls instead of sending them alone.
- Passed a new `prewalkArmed` session flag in `createAgentSession`, set from whether `prewalk` was supplied.

packages/coding-agent/CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Added per-agent prewalk for subagents: a `prewalk` frontmatter field (`true` = hand off to the default prewalk target, a string = custom target model pattern) and a `task.agentPrewalk` settings override toggled per agent from the `/agents` dashboard with `P`. The bundled generic `task` agent ships with prewalk enabled by default (skipped when the target resolves to the subagent's own starting model, and never armed for plan-mode spawns).
 
+### Changed
+
+- Batched todo operations with real tool calls to prevent solo todo turns and extra round trips
+
 ### Fixed
 
 - Fixed Bash internal URLs remaining unresolved when used as unquoted arguments inside command substitutions ([#5535](https://github.com/can1357/oh-my-pi/issues/5535)).

packages/coding-agent/src/prompts/system/system-prompt.md

@@ -193,6 +193,7 @@ EXECUTION WORKFLOW
 
 # 3. Decompose
 - Update todos as you go; skip them for trivial requests. Marking a todo done is a transition: start the next in the same turn.
+- Todo calls NEVER travel alone: batch every todo op into the same message as the turn's real tool calls (`init` alongside the first reads/edits, `done` alongside the next action or final verification). An assistant turn whose only tool call is todo wastes a full round trip.
 - Plan only what makes the request work. Cleanup—changelog, docs, removing scaffolding—is NOT planned up front; it belongs to the final phase below. Tests are cleanup only for permanent feature/bug-fix work (see Cleanup).
 
 # 4. Implement

packages/coding-agent/src/prompts/tools/todo.md

@@ -22,6 +22,7 @@ Completing tasks out of phase order can move this pointer **back** to an earlier
 
 ## Rules
 - Mark tasks done immediately after finishing. Complete phases in order.
+- NEVER make a todo call your turn's only tool call — batch it with the real work: `init` with the first reads/edits, each `done`/`start` with the next action. Solo todo turns waste a round trip.
 - Blocked? `append` a task to the active phase, or `drop`.
 - Keep `task`/`phase` strings stable once introduced.
 - Lost the exact task text? `view` echoes the list — NEVER guess from memory.

packages/coding-agent/src/sdk.ts

@@ -1590,6 +1590,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 			eventBus,
 			outputSchema: options.outputSchema,
 			requireYieldTool: options.requireYieldTool,
+			prewalkArmed: options.prewalk !== undefined,
 			taskDepth: options.taskDepth ?? 0,
 			getSessionFile: () => sessionManager.getSessionFile() ?? null,
 			getEvalKernelOwnerId: () => evalKernelOwnerId,