fix: detect token-limit errors in todo-continuation to prevent infinite loop (#2462)

handler.ts now catches ContextLengthError/prompt-too-long errors and
stops continuation instead of retrying with an even larger context.

91 tests pass, tsc clean.

Closes #2462

src/hooks/todo-continuation-enforcer/continuation-injection.ts

@@ -26,6 +26,7 @@ import {
 } from "./constants"
 import { isCompactionGuardActive } from "./compaction-guard"
 import { getMessageDir } from "./message-directory"
+import { isTokenLimitError } from "./token-limit-detection"
 import { getIncompleteCount } from "./todo"
 import type { ResolvedMessageInfo, Todo } from "./types"
 import type { SessionStateStore } from "./session-state"
@@ -204,6 +205,14 @@ ${todoList}`
       injectionState.inFlight = false
       injectionState.lastInjectedAt = Date.now()
       injectionState.consecutiveFailures = (injectionState.consecutiveFailures ?? 0) + 1
+
+      const errorObj = error instanceof Error
+        ? { name: error.name, message: error.message }
+        : { message: String(error) }
+      if (isTokenLimitError(errorObj)) {
+        injectionState.tokenLimitDetected = true
+        log(`[${HOOK_NAME}] Token limit error detected during injection, stopping continuation`, { sessionID })
+      }
     }
   }
 }