diff --git a/docs/fleet/north-star.md b/docs/fleet/north-star.md
index 22b6857..2e6dbba 100644
--- a/docs/fleet/north-star.md
+++ b/docs/fleet/north-star.md
@@ -115,6 +115,11 @@ Every artifact, starting Phase 2, MUST:
 - Observation: **read-only default, opt-in takeover**.
 - Multi-host: **designed-for from day one**; control plane **rides federation (W1)**.
 - Delivery: **CLI-first now**, dogfood against the live stub fleet; webUI deferred to Phase 5.
+- Runtimes: fleet agents default to **Codex / pi-on-Codex**; **Claude is reserved for Claude
+  Code only** (avoid alternate-harness API pricing). Validated durable recipe:
+  `mosaic yolo pi --model openai-codex/gpt-5.5:high`. Durable detached launch requires the
+  runtime-bin on PATH (baked into the pane command) + boot-survival (`enable` + linger),
+  which `fleet init` should automate.
 
 ## Assumptions (veto-able)
 
diff --git a/docs/scratchpads/fleet-observability-phase2.md b/docs/scratchpads/fleet-observability-phase2.md
index 22f0694..e499f6d 100644
--- a/docs/scratchpads/fleet-observability-phase2.md
+++ b/docs/scratchpads/fleet-observability-phase2.md
@@ -73,3 +73,28 @@ with a second agent on `dragon-lin`.
      tmux session-name fallback; the systemd/tmux env handoff needs a real fix.
 - Next: rebase on merged main, open Phase-2 PR, dual-engine review, merge, close
   `fleet-observability-1`. Defer launch-path + env-propagation fixes to Phase 3.
+- 2026-06-21 (session 3): Phase-2 PR #579 merged (3 dual-engine rounds hardened
+  verify+watch). Then closed the launch-path question with Jason's input — CORRECTING
+  earlier findings:
+  - The ad-hoc launch deaths were NOT a fundamental TTY blocker: (a) codex was a stale
+    version (Jason updated it); (b) pi was misconfigured to Claude auth (Jason removed it;
+    default is now Codex). The REAL durable-launch bug is **PATH**: the detached tmux
+    launch shell is login+non-interactive, so it misses `~/.npm-global/bin` (added only in
+    `~/.bashrc`) -> `mosaic: command not found` (127) -> pane dies. tmux panes inherit the
+    tmux _server_ env, so PATH must be baked into the pane command.
+  - **Durable real-agent recipe (validated live on gpt-5.5, Claude-free):**
+    `mosaic yolo pi --model openai-codex/gpt-5.5:high` — pi tolerates detached tmux; a raw
+    interactive TUI (codex CLI) exits without an attached client. Status line confirmed
+    `(openai-codex) gpt-5.5 • high`.
+  - PATH fix landed in `start-agent-session.sh` (commit 32efc13, branch
+    feat/fleet-launch-path): derive runtime-bin prefix (MOSAIC_RUNTIME_BIN | npm prefix |
+    ~/.npm-global/bin | ~/.local/bin), bake `export PATH=...; exec <cmd>` into the pane;
+    `exec` also fixes the drift false-positive. Live-tested under stripped PATH -> durable.
+  - Boot-survival: Jason ran `systemctl --user enable` (+ linger). TODO: auto-enable in
+    **fleet init** so operators never have to remember it (agentic-enhancement cycle).
+  - Future custom Pi harness build: pi cannot self-report its model (track
+    runtime/model/effort as fleet metadata); drift detection should recognize `node` as
+    pi's pane command (a node-wrapped pane can currently read as drift).
+  - Findings recorded in AI Guide playbooks/tmux-fleet.md (aiguide PR #7, merged).
+  - Policy: avoid Claude outside Claude Code (API pricing for alt-harness use) — fleet
+    runtimes default to Codex / pi-on-Codex; Claude stays in Claude Code only.