[BUG] Channel-notification turns (--dangerously-load-development-channels) not written to session JSONL in 2.1.172/2.1.173

What happened

A turn driven by a channel notification (notifications/claude/channel, delivered via an MCP stdio server with --dangerously-load-development-channels) runs to completion — the agent reads context, calls tools, and produces its answer — but no session JSONL transcript is ever written to disk for that turn. The session project directory under ~/.claude/projects/<encoded-cwd>/ is created (it contains a memory/ subdir), but the <session-id>.jsonl file never appears, even though the running agent's own status line cites that exact filename.

Typed/interactive turns and -p turns still write transcripts normally. Only channel-notification-driven turns vanish from disk.

This breaks any harness that observes agent activity by tailing the session transcript: the agent answers correctly, but there is no on-disk record of the turn (no user/assistant entries, no turn_ended), so the supervising process is blind to work that actually happened.

Version boundary

Controlled A/B against the same harness — the only variable is the claude binary:

| Version | Channel-turn transcript written? |
|---|---|
| 2.1.170 | ✅ yes (works) |
| 2.1.172 | ❌ no |
| 2.1.173 | ❌ no |

2.1.173 does not fix it. Pinning to ≤ 2.1.170 is the only workaround we've found.

Minimal evidence (2.1.173)

• The agent ran a full turn and posted its answer via an MCP tool — confirmed in its tmux pane.
• The agent's status line referenced session b606e37e-…jsonl.
• find ~/.claude/projects -name 'b606e37e-….jsonl' → no such file anywhere on disk.
• The session project dir ~/.claude/projects/-private-tmp-…-project/ contained only an empty memory/ subdir — no .jsonl.

This looks like the same class as prior persistence regressions

• #60984 — 2.1.144/2.1.145: JSONL contained only an ai-title stub, no message content; fixed by downgrading to 2.1.143.
• #66486 — 2.1.169: interactive sessions wrote only an ai-title stub (regressed from 2.1.168).

Same fingerprint: a session-persistence rework that stops flushing real turn content to the transcript. This report is the channel-notification-turn variant, newly present in 2.1.172 and still present in 2.1.173.

Steps to reproduce

1. Launch claude with --dangerously-load-development-channels server:<name> and an MCP stdio server that advertises the claude/channel capability.
2. From that MCP server, push a notifications/claude/channel notification instructing the agent to do some work and respond.
3. Observe: the agent completes the turn and answers, but ~/.claude/projects/<encoded-cwd>/<session-id>.jsonl is never created.
4. Repeat with 2.1.170 → the transcript is written.

Environment

• Claude Code: 2.1.172 and 2.1.173 (broken); 2.1.170 (good)
• OS: macOS 26.4 (arm64)
• Node: v25.9.0

Expected

Channel-notification-driven turns should be persisted to the session JSONL transcript exactly like typed/-p turns are.