fix(run): prevent premature exit on idle before meaningful work (#1263)

The run command's completion check had a race condition: when a session
transitions busy->idle before the LLM generates any output (empty
response or API delay), checkCompletionConditions() returns true because
0 incomplete todos + 0 busy children = complete. This caused the runner
to exit with 'All tasks completed' before any work was done.

Fix:
- Add hasReceivedMeaningfulWork flag to EventState
- Set flag on: assistant text content, tool execution, or message update
  with actual content (all scoped to main session only)
- Guard completion check in runner poll loop: skip if no meaningful work
  has been observed yet

This ensures the runner waits until the session has produced at least one
observable output before considering completion conditions.

Adds 6 new test cases covering the race condition scenarios.

src/cli/run/events.ts

@@ -63,6 +63,8 @@ export interface EventState {
   lastOutput: string
   lastPartText: string
   currentTool: string | null
+  /** Set to true when the main session has produced meaningful work (text, tool call, or tool result) */
+  hasReceivedMeaningfulWork: boolean
 }
 
 export function createEventState(): EventState {
@@ -73,6 +75,7 @@ export function createEventState(): EventState {
     lastOutput: "",
     lastPartText: "",
     currentTool: null,
+    hasReceivedMeaningfulWork: false,
   }
 }
 
@@ -241,6 +244,7 @@ function handleMessagePartUpdated(
     const newText = part.text.slice(state.lastPartText.length)
     if (newText) {
       process.stdout.write(newText)
+      state.hasReceivedMeaningfulWork = true
     }
     state.lastPartText = part.text
   }
@@ -267,6 +271,7 @@ function handleMessageUpdated(
     }
   }
   state.lastOutput = content
+  state.hasReceivedMeaningfulWork = true
 }
 
 function handleToolExecute(
@@ -296,6 +301,7 @@ function handleToolExecute(
     }
   }
 
+  state.hasReceivedMeaningfulWork = true
   process.stdout.write(`\n${pc.cyan(">")} ${pc.bold(toolName)}${inputPreview}\n`)
 }