feat(#20): characters + me/capabilities/models onto the wt adapter (slice-5)

Slice-5 of the worldtree-sdk cutover: migrate the remaining consumer READS +
transient-character CRUD off the hand-rolled httpx wrappers onto the
`ratatoskr.wt` adapter over the SDK, and delete the retired path.

Adapter (`wt.py`): add `get_me` / `get_capabilities` / `list_character_models`
/ `create_character` / `get_character_state` / `delete_character` over
`client.me` / `client.capabilities` / `client.models` / `client.characters.*`.
All six are open-world reads/acks returned verbatim; none carries a
discriminated SDK error, so each maps any `ApiError` → the `SessionApiFailed`
default (INV-CUT-2) — exact parity with the retired path. No new Error-map rows.

Decisions (contract § slice-5 notes): `create_character` omits `state` when None
(SDK-idiomatic inline literal, server-equivalent to the retired explicit null);
`delete_character` returns the SDK's open ACK verbatim (`-> Mapping|None`, not
normalized to None).

CLI rewire (`cli.py`): `--whoami` (me + capabilities) and `--characters`
(models → create → state → delete) build a `wt.build_client` over the injected
probe transport and catch `wt.SessionApiFailed` + `ConnectFailed`. Open-world
degrade-not-crash carried (cumulative cutover foot-gun): `_characters_probe`
reads `items` null-safe and extracts `character_id` defensively (clean abort,
no hard-index KeyError); `_format_whoami` widened to `Mapping`.

Deleted the six hand-rolled `sessions.py` wrappers (net -5 mypy no-any-return);
`endpoint_for_plane` + `get_session_bifrost` (slice-6) + the exception classes
stay. Retired the corresponding `test_sessions.py` classes; added the slice-5
adapter tests + a CLI malformed-create-abort test.

LIVE SMOKE (:8081, b128) — INV-CUT-5 / DEC-4 cleared: `--whoami` rendered real
identity + capabilities; `--characters` drove the full lifecycle end-to-end
(char-rp catalog → created char_8c00006e… → PAD read-back → deleted).

Suite 483 green; ruff clean; mypy at the 2 pre-existing baseline errors.
Patch bump 0.21.15 → 0.21.16 (the cutover MINOR is deferred to slice-7, DEC-6).

docs/coverage-map.md

@@ -94,15 +94,15 @@ sub-gap).
 | `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 /me` | ✅ | `wt.py` `get_me` (SDK `me.get`) → `cli.py` `--whoami` | **wt-adapter re-anchored (slice-5, #20)** — open-world identity dict verbatim; any error→SessionApiFailed default (401 on a bad/absent key), transport→ConnectFailed→exit 21. **LIVE-SMOKE 2026-07-19** on personal :8081 (b128): identity rendered (user_id ratatoskr, tier user, scopes incl. `character.*`, key_id c990f0be) |
+| `GET /capabilities` | ✅ | `wt.py` `get_capabilities` (SDK `capabilities.get`) → `cli.py` `--whoami` | **wt-adapter re-anchored (slice-5, #20)** — open-world advertisement verbatim; `_format_whoami` reads `allowed_roles`/`default_role` and degrades on a null/non-mapping template (slice-4 hardening); matches conversation-api-spec **v1.1** (`b4a278c`). **LIVE-SMOKE 2026-07-19**: `ephemeral_template echo: default=echo max_bytes=32768 roles=[echo]` |
 | `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) |
 | `GET /admin/sessions/{id}/bifrost` | ✅ | `sessions.py:428` `get_session_bifrost` → `tui.py` `_hydrate_bifrost_state` | admin-scoped BifrostState pane (#176); admin key (`RATATOSKR_ADMIN_API_KEY`); live-auth-proven |
 | `GET /admin/events` (SSE) | ✅ | `sse_client.py` `stream_admin_events` → `tui.py` `_stream_admin_events` | admin lifecycle SSE stream (#11), session-filtered AdminEvents pane; admin key; live-auth-proven |
-| `GET /models/available-for-characters` | ✅ | `sessions.py` `list_character_models` → `cli.py` `--characters` | character-capable model profiles (#161) |
-| `POST /characters` | ✅ | `sessions.py` `create_character` → `cli.py` `--characters` | create transient character (#161) |
-| `GET /characters/{id}/state` | ✅ | `sessions.py` `get_character_state` → `cli.py` `--characters` | live character PAD/emotions (#161) |
-| `DELETE /characters/{id}` | ✅ | `sessions.py` `delete_character` → `cli.py` `--characters` | remove transient character (#161) |
+| `GET /models/available-for-characters` | ✅ | `wt.py` `list_character_models` (SDK `models.available_for_characters`) → `cli.py` `--characters` | **wt-adapter re-anchored (slice-5, #20)** — open-world catalog verbatim; the probe reads `items` null-safe (`or []`); any error→SessionApiFailed default. **LIVE-SMOKE 2026-07-19**: `character models: char-rp` |
+| `POST /characters` | ✅ | `wt.py` `create_character` (SDK `characters.create`) → `cli.py` `--characters` | **wt-adapter re-anchored (slice-5, #20)** — body `{character}` (+`state` only when set — SDK-idiomatic, drops the redundant explicit null); open-world create ACK verbatim; the probe degrades on a missing `character_id` (no hard-index). **LIVE-SMOKE 2026-07-19**: `created char_8c00006e…` |
+| `GET /characters/{id}/state` | ✅ | `wt.py` `get_character_state` (SDK `characters.state`) → `cli.py` `--characters` | **wt-adapter re-anchored (slice-5, #20)** — open-world live PAD/emotions verbatim; TTL-refreshing read. **LIVE-SMOKE 2026-07-19**: `state pad=[0.234, -0.136, 0.065]` read back |
+| `DELETE /characters/{id}` | ✅ | `wt.py` `delete_character` (SDK `characters.delete`) → `cli.py` `--characters` | **wt-adapter re-anchored (slice-5, #20)** — returns the SDK's open ACK verbatim (`-> Mapping|None`, NOT normalized to None; 204→None); any error→SessionApiFailed default. **LIVE-SMOKE 2026-07-19**: `deleted char_8c00006e…` |
 | `POST /sessions/{id}/persona_state` | ✅ | `wt.py` `set_persona_state` (SDK `sessions.set_persona_state`, `PadState`) → `cli.py` `--set-persona-pad` | **wt-adapter re-anchored (slice-3, #20)** — SDK owns the canonical `{"pad": {...}}` wire (#317); CLI passes the 3 PAD axes (finiteness pre-validated); 204→None, else SessionApiFailed default. **LIVE-SMOKE 2026-07-19** on personal :8081: `--set-persona-pad 0.4,0.1,-0.2` → **204** |
 
 **Sub-gaps inside ✅ path groups** (the method we use is live; a sibling method