feat(#20): agents/tier3 family onto the wt adapter + model→role fold (slice-4)

Cut ratatoskr's consumer agent-lifecycle routes over to worldtree-sdk
(issue #20 slice-4). Five routes now flow through `ratatoskr.wt` over the
SDK's `client.agents.*`, returning open-world dicts and mapping the SDK's
undiscriminated `ApiError` floor by route+(status,error_code) per INV-CUT-2:

- `list_agents`      → `agents.list`
- `get_persona_state`→ `agents.persona_state` (404 persona_not_configured /
                        404 agent_not_available / 403 auth_scope_denied)
- `define_agent`     → `agents.define` (429→Tier3QuotaExceeded(retry_after=0),
                        403→Tier3UserIdUnsupported, 422 layer_deferred→…)
- `patch_agent`      → `agents.patch`  (404→Tier3AgentNotFound, 422 field_not_mutable)
- `delete_agent`     → `agents.delete` (404→Tier3AgentNotFound; NOT hide-existence)

Rewired call-sites: the `python -m ratatoskr.tier3` CLI (define/patch/delete)
and the web `_agents_endpoint` / `_persona_state_endpoint`, both catching the
SDK's `ConnectFailed` transport-failure normalization. Deleted the hand-rolled
paths: `sessions.list_agents` / `get_persona_state` / `AgentInfo`, and
`tier3.define/patch/delete_agent` / `Tier3AgentInfo` / parse+extract helpers.

model→role fold (scope B): the define/patch response echoes `role` (spec 1.2 /
b128), read off the open-world dict; `LocalAgentEntry.model`→`.role`,
local-index schema v1→2 (old index discarded, no-backwards-compat).

The Tier-3 caller-semantic exceptions move to `sessions.py`: running the CLI
as `__main__` while `wt` imports `ratatoskr.tier3` bound two copies of each
exception class, so a raised `Tier3AgentNotFound` escaped the CLI's `except`
as an uncaught traceback. Homing them in `sessions` (never `__main__`) makes
the class identity single. The live smoke — not the unit tests, which call
`main()` in-process — caught this.

Error-map rows + slice-4 notes added to the cutover contract; coverage-map
re-anchored. LIVE-SMOKE on personal :8081 (b128): define(thoughtful-character)
→ patch → list(6 agents) → persona_state(→PersonaNotConfigured mapped) →
delete → index empty; non-existent-id patch via `-m` → [agent_not_found]
exit 20. Suite 465 green.

docs/coverage-map.md

@@ -89,11 +89,11 @@ sub-gap).
 | `POST /sessions/{id}/history` (authored-history-write, #347) | ✅ | `wt.py` `write_authored_history` (SDK `sessions.write_history`) → `cli.py` `--seed-first-message`, `first_message.py` `seed_preset_first_message` (create-path seed) | **wt-adapter re-anchored (slice-3, #20)** — SDK owns the entry shape; v1 author=assistant; 404→AuthoredHistoryUnavailable (hide-existence, route is the discriminator, never probe); 409/422→SessionApiFailed default. **LIVE-SMOKE 2026-07-19** on personal :8081 (b128): `--seed-first-message` on a sindra session → **201** (seq=0, phase=seeded, turn_id=2294) → read-back verbatim; create-path preset seed observed via `--new`. (Prior 2026-07-06 hand-rolled proof superseded.) |
 | `GET /sessions/{id}/messages` (history) | ✅ | `wt.py` `get_session_messages` (SDK `sessions.messages`) → `cli.py` `--seed-first-message` read-back, `web/server.py` messages proxy | **wt-adapter re-anchored (slice-3, #20)** — the #347 seed read-back; open-world passthrough. **LIVE-SMOKE 2026-07-19**: read-back rendered the seeded seq-0 turn as a plain role=assistant message (model-invisible provenance confirmed) |
 | `POST /sessions/{id}/turns/{turn_id}/cancel` | ✅ | `wt.py` `cancel_turn` (SDK `sessions.cancel_turn`) → cli/web | **wt-adapter re-anchored (slice-2, #20)** — two-stage Ctrl-C; 404→CancelTurnNotFound, 409→CancelAlreadyCompleted, late-cancel 200 (`cancelled=False`) is a benign result, not an error |
-| `GET /agents` | ✅ | `sessions.py:341` → `tui.py:1472`,`web/server.py:100` | Tier-1 roster; merged with local index |
-| `GET /agents/{id}/persona_state` | ✅ | `sessions.py:384` → `tui.py:1132`,`web/server.py:386` | persona hydrate; 404/403 mapped |
-| `POST /agents/define` | ✅ | `tier3.py:175` → `_run_define` | Tier-3 create |
-| `PATCH /agents/{id}` | ✅ | `tier3.py:219` → `_run_patch` | Tier-3 mutate (system_prompt/model) |
-| `DELETE /agents/{id}` | ✅ | `tier3.py:242` → `_run_delete` | Tier-3 hard-delete |
+| `GET /agents` | ✅ | `wt.py` `list_agents` (SDK `agents.list`) → `web/server.py` `_agents_endpoint` | **wt-adapter re-anchored (slice-4, #20)** — open-world array verbatim (no AgentInfo normalization), merged with the local tier3 index (remote-wins); error→SessionApiFailed default, transport→ConnectFailed→502. **LIVE-SMOKE 2026-07-19** on personal :8081 (b128): 6 agents returned (forseti/lofn/mask/mimir/vili/…) |
+| `GET /agents/{id}/persona_state` | ✅ | `wt.py` `get_persona_state` (SDK `agents.persona_state`) → `web/server.py` `_persona_state_endpoint` | **wt-adapter re-anchored (slice-4, #20)** — open-world snapshot; dual-key (status,error_code) map: 404 persona_not_configured→PersonaNotConfigured, 404 agent_not_available→AgentNotAvailable, 403 auth_scope_denied→AuthScopeDenied, else default. **LIVE-SMOKE 2026-07-19**: a tier3 agent → correctly mapped `PersonaNotConfigured` (route+code adapter proven) |
+| `POST /agents/define` | ✅ | `wt.py` `define_agent` (SDK `agents.define`) → `tier3.py` `_run_define` | **wt-adapter re-anchored (slice-4, #20)** — sends AgentDefineInput `{agent_name,role,system_prompt}`, returns open-world `DefinedAgent` (echoes `role`, b128); slug pre-validated; 429→Tier3QuotaExceeded(retry_after=0, header-less floor), 403→Tier3UserIdUnsupported, 422 layer_deferred→Tier3LayerDeferred. **LIVE-SMOKE 2026-07-19**: `define --role thoughtful-character` → `defined ratatoskr:slice4-smoke (thoughtful-character)` |
+| `PATCH /agents/{id}` | ✅ | `wt.py` `patch_agent` (SDK `agents.patch`) → `tier3.py` `_run_patch` | **wt-adapter re-anchored (slice-4, #20)** — Tier-3 mutate (system_prompt/**role**, model→role folded in); 404→Tier3AgentNotFound, 422 field_not_mutable→Tier3FieldNotMutable. **LIVE-SMOKE 2026-07-19**: `patched ratatoskr:slice4-smoke`; a non-existent id via `python -m` → `[agent_not_found]` (exit 20, class-identity fix proven) |
+| `DELETE /agents/{id}` | ✅ | `wt.py` `delete_agent` (SDK `agents.delete`) → `tier3.py` `_run_delete` | **wt-adapter re-anchored (slice-4, #20)** — 204→None; 404→Tier3AgentNotFound (route-discriminated, NOT hide-existence). **LIVE-SMOKE 2026-07-19**: `deleted ratatoskr:slice4-smoke` + local index → `[]` |
 | `GET /me` | ✅ | `sessions.py:411` `get_me` → `cli.py` `--whoami` | identity/whoami probe; 401→SessionApiFailed |
 | `GET /capabilities` | ✅ | `sessions.py` `get_capabilities` → `cli.py` `--whoami` | Echo ephemeral-template discovery. **v0.21.2: `--whoami` renderer reads `allowed_roles`/`default_role`** (was the dead `allowed_models`/`default_model`) + tolerates malformed caps; matches conversation-api-spec **v1.1** (`b4a278c`) |
 | `GET /sessions/{id}/tools` | ✅ | `sessions.py:411` `get_session_tools` → `tui.py` `_hydrate_session_tools` | owner-scoped tool inventory in the TUI Tools pane (#183) |