🐛 fix: extract JSON from turn_end in PiAgent json mode NDJSON stream

[SamuelLHuber]

Problem

The usage of Dynamic Task Discovery with PiAgent is not working due to Pi's output not being parsed correctly into a task list.

When PiAgent uses mode: "json", pi outputs NDJSON (newline-delimited JSON) where:

• First object: Session metadata {"type":"session",...}
• Middle objects: Thinking tokens, progress updates
• Last object: turn_end containing the actual response

Previously, the code tried to parse the entire stdout as a single JSON object, which failed. The first line (session metadata) would be returned instead of the actual response.

Solution

Added extractTextFromPiNdjson() which:

1. Scans the NDJSON stream backwards
2. Finds turn_end or agent_end events
3. Extracts text from the assistant message content
4. Falls back to generic extraction for simple cases

Changes

• src/agents/cli.ts: Add extractTextFromPiNdjson() function, update PiAgent.generate()
• tests/pi-support.test.ts: Add 3 tests for NDJSON extraction

Testing

• ✅ Unit tests pass (8/8 in pi-support.test.ts)
• ✅ Verified with real pi --mode json
• ✅ TypeScript compiles cleanly

Example

Before:

text: {"type":"session","version":3,"id":"...",...}
output: { type: "session", ... }  // Wrong!

After:

text: {"v":1,"tickets":[...],"batchComplete":true}
output: { v: 1, tickets: [...], batchComplete: true }  // Correct!

[SamuelLHuber]

CI Status Note

The CI failures are pre-existing issues on the main branch, not related to this PR:

Failure	Cause
MergeQueue tests	MDX preload configuration issue
HTTP Server tests	Server connection issues in test environment

These same 12 tests fail on main branch (verified locally). This PR adds 3 new passing tests for the PiAgent json mode fix.

Verification

• ✅ TypeScript compiles cleanly
• ✅ 8/8 pi-support tests pass locally
• ✅ Tested with real pi --mode json
• ✅ No merge conflicts with main