fix: extract lib/formula-session.sh to eliminate duplicate code blocks

Shared helpers for formula-driven cron agents: lock, memory guard,
formula loading, context building, session startup, crash recovery.

- planner-run.sh uses shared helpers instead of inline code
- gardener-agent.sh delegates crash recovery to formula_phase_callback
- agent-smoke.sh updated for renamed planner script + new lib file

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -291,6 +291,7 @@ sourced as needed.
 | `lib/load-project.sh` | Parses a `projects/*.toml` file into env vars (`PROJECT_NAME`, `CODEBERG_REPO`, `WOODPECKER_REPO_ID`, monitoring toggles, Matrix config, etc.). | env.sh (when `PROJECT_TOML` is set), supervisor-poll (per-project iteration) |
 | `lib/parse-deps.sh` | Extracts dependency issue numbers from an issue body (stdin → stdout, one number per line). Matches `## Dependencies` / `## Depends on` / `## Blocked by` sections and inline `depends on #N` patterns. Not sourced — executed via `bash lib/parse-deps.sh`. | dev-poll, supervisor-poll |
 | `lib/matrix_listener.sh` | Long-poll Matrix sync daemon. Dispatches thread replies to the correct agent via well-known files (`/tmp/{agent}-escalation-reply`). Handles supervisor, gardener, dev, review, vault, and action reply routing. Run as systemd service. | Standalone daemon |
+| `lib/formula-session.sh` | `acquire_cron_lock()`, `check_memory()`, `load_formula()`, `build_context_block()`, `start_formula_session()`, `formula_phase_callback()` — shared helpers for formula-driven cron agents (lock, memory guard, formula loading, tmux session, crash recovery). | planner-run.sh |
 | `lib/file-action-issue.sh` | `file_action_issue()` — dedup check, label lookup, and issue creation for formula-driven cron wrappers. Sets `FILED_ISSUE_NUM` on success. | gardener-run.sh |
 | `lib/agent-session.sh` | Shared tmux + Claude session helpers: `create_agent_session()`, `inject_formula()`, `agent_wait_for_claude_ready()`, `agent_inject_into_session()`, `agent_kill_session()`, `monitor_phase_loop()`, `read_phase()`. `create_agent_session(session, workdir, [phase_file])` optionally installs a PostToolUse hook (matcher `Bash\|Write`) that detects phase file writes in real-time — when Claude writes to the phase file, the hook writes a marker so `monitor_phase_loop` reacts on the next poll instead of waiting for mtime changes. Also installs a StopFailure hook (matcher `rate_limit\|server_error\|authentication_failed\|billing_error`) that writes `PHASE:failed` with an `api_error` reason to the phase file and touches the phase-changed marker, so the orchestrator discovers API errors within one poll cycle instead of waiting for idle timeout. When `MATRIX_THREAD_ID` is exported, also installs a Stop hook (`on-stop-matrix.sh`) that streams each Claude response to the Matrix thread. `monitor_phase_loop` sets `_MONITOR_LOOP_EXIT` to one of: `done`, `idle_timeout`, `idle_prompt` (Claude returned to `❯` for 3 consecutive polls without writing any phase — callback invoked with `PHASE:failed`, session already dead), `crashed`, or a `PHASE:*` string. Agents must handle `idle_prompt` in both their callback and their post-loop exit handler. | dev-agent.sh, gardener-agent.sh, action-agent.sh |