Stop phantom-notification hangs and drop noisy "0초" progress label

Agents ended turns with "I'll wait … I'll be notified" expecting a
background-completion callback that this environment never delivers, so
the turn hung and left the planning sentence stuck in the channel. Add a
claude-platform rule that no such notification exists — finish within the
turn (foreground/poll) or ask the user for a follow-up.

Also suppress the elapsed-time suffix on progress messages until at least
one 5s bucket has elapsed, so freshly-created progress no longer shows a
meaningless "0초". Update the affected message-runtime expectations.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

prompts/claude-platform.md

@@ -5,6 +5,18 @@ Use it to acknowledge a request before starting longer work.
 
 When working as a sub-agent or teammate, only use `send_message` if the main agent explicitly asked you to.
 
+## Background work never notifies you — finish within the turn
+
+Nothing in this environment re-invokes you when a background process, a background shell command, or a `run_in_background` job finishes. You will NOT be automatically notified when a build, compile, download, deploy, or any background task completes. The built-in tool descriptions that say "you'll be notified when it finishes" do NOT apply here.
+
+If you end your turn with a sentence like "I'll wait for the build to complete — I'll be notified", the turn simply ends and nothing ever resumes — the user is left stuck staring at that message. This is a real, repeated failure. Do not do it.
+
+Therefore:
+
+- Do not launch long work in the background and then end the turn expecting a callback. Run it in the foreground and block/poll until it actually finishes inside this same turn, then report the real result.
+- If something genuinely cannot complete within one turn, do not pretend a notification is coming. Finish with a concrete status and explicitly ask the user to send a follow-up message to continue. For recurring polling of CI/scheduled work, use the `schedule_task` / `watch_ci` tools, which DO re-invoke you.
+- Never leave an intermediate "I'll wait … I'll be notified" planning sentence as your final answer.
+
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