story-kit: create 131_bug_get_agent_output_stream_always_times_out_for_running_agents

.story_kit/work/1_upcoming/131_bug_get_agent_output_stream_always_times_out_for_running_agents.md

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+---
+name: "get_agent_output stream always times out for running agents"
+---
+
+# Bug 131: get_agent_output stream always times out for running agents
+
+## Description
+
+The `get_agent_output` MCP tool consistently returns "Stream timed out; call again to continue" even when the agent process is actively running, making API calls, and committing work. The `list_agents` call shows the agent as `running` with `session_id: null` throughout its entire execution, only populating the session_id after the process exits. This makes it impossible to observe agent progress in real time via MCP.
+
+## How to Reproduce
+
+1. Start an agent on a story (e.g. `start_agent` with `coder-1`)
+2. Confirm the claude process is running (`ps aux | grep claude`)
+3. Call `get_agent_output` with the story_id and agent_name
+4. Observe it returns "Stream timed out" every time, regardless of timeout_ms value (tested up to 10000ms)
+5. `list_agents` shows `session_id: null` throughout
+6. Agent completes its work and commits without ever producing observable output
+
+## Actual Result
+
+`get_agent_output` never returns any events. `session_id` stays null while the agent is running. The only way to observe progress is to poll the worktree's git log directly.
+
+## Expected Result
+
+`get_agent_output` streams back text tokens and status events from the running agent in real time. `session_id` is populated once the agent's first streaming event arrives.
+
+## Acceptance Criteria
+
+- [ ] get_agent_output returns streaming text events while an agent is actively running
+- [ ] session_id is populated in list_agents shortly after agent spawn
+- [ ] Calling get_agent_output multiple times yields incremental output from the agent