feat(sessions,cli,tui): issue #8 — startup agent picker (v0.3.0)

Adds GET /agents fetch + ListView picker for bare `--new` (TUI mode
without --agent). Three in-place amendments:

- ratatoskr.sessions: new `list_agents()` + `AgentInfo` frozen
  dataclass with omit-when-null/empty defaults mirroring SessionInfo's
  INV-001/INV-002 origin-conditional pattern. Non-200 responses raise
  the existing SessionApiFailed (no new exception).
- ratatoskr.cli: `_parse_args` softens `--agent` from absolute to
  mode-conditional — required for `--send --new`, optional for bare
  `--new`, forbidden with `--session` (unchanged INV-004).
- ratatoskr.tui: new `AgentPickerApp(App[str | None])` — separate
  Textual App (not Screen-within-RatatoskrApp) so list_agents errors
  land on real stderr before any alt-screen opens (preserves issue
  #6's INV-001). `_resolve_then_run` gains a pre-create branch:
  fetch agents → empty list → exit 13; non-200 → exit 20; network
  error → exit 21; picker dismissed → exit 0; otherwise thread chosen
  agent_id into create_session.

Contract: docs/contracts/issues/8.contract.md (drift-check clean).

Tests: +18 (227 total, was 209). Live smoke against personal Worldtree
(:8081) returned 12 agents; programmatic picker drive auto-picked lofn
and created a real session with `end_user_id="ratatoskr-tui"`.

persistent-memory.md

@@ -1,6 +1,6 @@
 # Persistent memory — ratatoskr
 
-_Last updated: 2026-05-23_
+_Last updated: 2026-05-24_
 
 This file captures durable intent and supporting evidence (goals, decisions,
 foot-gun warnings, in-flight state) across context resets. Read it at session
@@ -32,51 +32,47 @@ separate dev team rather than an in-tree Worldtree tool.
 
 ## Current state / in-flight
 
-_As of 2026-05-23 (end of day, post-v0.2.1 layout fix):_
+_As of 2026-05-24 (post-v0.3.0 startup agent picker):_
 
-**Status: v0.2.0 + v0.2.1 shipped and pushed.** Seven core issues
-complete (`sse_client` #1, `sessions` #2, `cli` #3, `tui` #4,
-`--end-user-id` #5, TUI startup error visibility #6, presenter
-contract semantics amendment #12) + robustness fix #7 (MalformedSseData
-+ empty-skip) + v0.2.1 TUI layout fix on top. 209/209 tests GREEN;
-ruff clean; working tree clean; both v0.2.0 and v0.2.1 tags on
-`origin/main`.
+**Status: v0.3.0 shipped.** Eight core issues complete (`sse_client`
+#1, `sessions` #2, `cli` #3, `tui` #4, `--end-user-id` #5, TUI
+startup error visibility #6, presenter contract semantics amendment
+#12, startup agent picker #8) + robustness fix #7 (MalformedSseData
++ empty-skip) + v0.2.1 TUI layout fix. 227/227 tests GREEN; ruff
+clean.
 
 Last commits on `main`:
+- v0.3.0 feat(sessions,cli,tui): issue #8 — startup agent picker
 - `c85f6bd` fix(tui): anchor layout via dock so Input never moves (v0.2.1)
 - `3b9c610` feat(cli,tui): issue #12 — presenter contract semantics amendment (v0.2.0)
 - `8282156` snapshot: persistent-memory Heimdall scope-model foot-gun
 - `804c2df` feat(sessions,cli,tui): issues #5 + #6 + worldtree-dev follow-up (v0.1.0)
 
 **Smoke status:**
-- `--send` v0.1.0 mimir smoke clean earlier today (`[done] turn_id=116
-  duration_ms=5467`).
-- `--send` v0.2.0 mimir smoke survived a Worldtree-side stall (see
-  Tried-and-abandoned for the 2-events-then-silence diagnostic shape).
-  After worldtree-dev's operator-side `:8081` restart, mimir responded
-  cleanly with the new v0.2.0 rendering shape: coalesced thinking
-  runs, `. ` ASCII prefix for demoted telemetry, `duration=11.8s` /
-  `usage 40764 in -> 850 out (41614 total, 0 cached)` formatting.
+- `--send --new --agent mimir` v0.3.0 smoke clean
+  (`[done] turn_id=141 model=qwen3.6-35-a3b duration=2.2s`).
+- Live `list_agents` smoke against personal Worldtree returned 12
+  agents (actor, bragi, cara, domari, forseti, glados, leif, lofn,
+  mimir, soong, troi, saga).
+- Picker end-to-end smoke against live Worldtree: bare `--new` →
+  list_agents → picker (auto-picked lofn programmatically since
+  driving alt-screen interactively from CLI smoke isn't possible)
+  → POST /sessions with end_user_id="ratatoskr-tui" succeeded;
+  RatatoskrApp constructed with agent_id="lofn".
 - TUI v0.2.0 was visually broken (Input pane bouncing with thinking
   runs); v0.2.1 fixed via dock-based layout. Operator confirmed
   "a lot better" interactively.
-- Lofn smoke is **auth-unblocked** (Tier 1 agent.call:* baseline
-  covers it; the phantom-scope-add diagnosis is settled in
-  Tried-and-abandoned). Not yet run.
 
 **Outstanding operator-side todos:**
-- **Post-v0.2.1 lofn smoke** — `source env.sh && uv run ratatoskr
-  --new --agent lofn --send "hello"`. Now unblocked on auth.
+- **Interactive TUI picker eyeball** — `source env.sh && uv run
+  ratatoskr --new` (no flags after) should show the picker; pick
+  lofn; type a message; verify response streams cleanly. Auto-pick
+  smoke confirmed the wiring; visual confirmation pending.
 - **Post-v0.2.1 TUI multi-turn eyeball** — confirm thinking-run
   bouncing is gone across multiple turns; the layout fix has only
   been confirmed for a single turn so far.
 
 **Pending issues filed but not started:**
-- **Issue #8 (startup agent picker)** — filed but unscaffolded.
-  Worldtree-dev confirmed `GET /agents` requires no special scope;
-  auth side is unblocked. Composes with #5 (both thread through
-  `ParsedArgs` → `_resolve_then_run`). **This is the next planned
-  feature** (see Recent decisions §5-sequencing).
 - **Issue #9 (spec-pin refresh v0.19.0 → v0.22.1)** — filed
   2026-05-23. Documentation debt; defer unless we need a v0.20.0+
   capability.
@@ -101,15 +97,14 @@ Branch: `main` (clean). Remote:
 
 **Next natural moves:**
 
-1. **Lofn smoke** — quick operator-side eyeball.
-2. **Issue #8 (startup agent picker)** — scaffold + contract +
-   TDD. Independent of layout work; gates §5 side-panes work per
-   the 2026-05-23 sequencing decision.
-3. **§5 side-panes work** — Persona pane first per design-brief; the
+1. **Interactive picker eyeball** — operator confirms the TUI
+   picker UX (rendering, Enter pick, Esc dismiss) against personal
+   Worldtree.
+2. **§5 side-panes work** — Persona pane first per design-brief; the
    collapsible Thinking pane + Debug pane proposals fold IN as
    additional `TabbedContent` tabs alongside Persona/Tools/AdminEvents.
    Reshapes layout from vertical-stack to Horizontal two-column.
-4. **Issue #9 (spec-pin refresh)** — defer unless we need a v0.20.0+
+3. **Issue #9 (spec-pin refresh)** — defer unless we need a v0.20.0+
    capability (e.g., `memory_context` for Phase 2.1).
 
 ## Recent decisions