fix(todo-continuation): remove activity-based stagnation bypass

Activity signals (tool calls like compress, grep, bash) were treated as
'progress' by the stagnation detector, resetting the stagnation counter
every cycle. This prevented MAX_STAGNATION_COUNT from being reached,
causing infinite continuation loops when models degrade to minimal
responses in long sessions (e.g. GLM-5.1 at ~100K tokens).

Stagnation now only tracks actual todo state changes: incomplete count
decrease, completed count increase, or todo snapshot change. Tool-level
activity no longer resets the stagnation counter.

src/hooks/todo-continuation-enforcer/idle-event.ts

@@ -16,14 +16,6 @@ import { acknowledgeCompactionGuard, isCompactionGuardActive } from "./compactio
 import type { SessionStateStore } from "./session-state"
 import { startCountdown } from "./countdown"
 
-function shouldAllowActivityProgress(modelID: string | undefined): boolean {
-  if (!modelID) {
-    return false
-  }
-
-  return !modelID.toLowerCase().includes("codex")
-}
-
 export async function handleSessionIdle(args: {
   ctx: PluginInput
   sessionID: string
@@ -204,7 +196,6 @@ export async function handleSessionIdle(args: {
     sessionID,
     incompleteCount,
     todos,
-    { allowActivityProgress: shouldAllowActivityProgress(resolvedInfo?.model?.modelID) },
   )
   if (shouldStopForStagnation({ sessionID, incompleteCount, progressUpdate })) {
     return