agents: remove the hive-level /model control; the swarm editor sets the model

The per-agent web UI no longer sets the model: the `/model` slash
command, the model picker, `POST /api/model`, `Bus::set_model` and the
`hyperhive-model` writer are gone. The model chip is display-only and
shows where the model comes from (`model_source` in `/api/state`). The
model is set on the swarm (swarm UI agents page, `swarmctl agent
inference set`).

The read side is unchanged: with no swarm value an agent runs its
agent.nix model, else an existing `hyperhive-model` file, else haiku.
Existing files are not touched.

With the picker gone, its model list goes too: `available_models` in
`/api/state`, the ACP model-list filter, and the harness's global
`HIVE_AVAILABLE_MODELS`. The subagent daemon keeps its own
`HIVE_AVAILABLE_MODELS` from mcp.nix, and the `availableModels`
assertion stays.

`/effort` (command, picker, route, file) is unchanged.

Refs #5034

docs/agent-lifecycle/persistence.md

@@ -211,12 +211,12 @@ log row never blocks a rebuild.
 
 ### `/harness/hyperhive-model` (per agent)
 
-Single-line text file holding the claude model name currently
-selected for this agent (default `haiku` when absent). Written by
-`Bus::set_model` whenever the operator flips it via `/model
-<name>` in the web terminal. Read once at harness boot in
-`Bus::new`. Path overridable via `HYPERHIVE_MODEL_FILE`.
-Survives destroy/recreate, gone on `--purge`.
+Single-line text file holding a claude model name. The harness only
+reads it, at boot in `Bus::new` and again when the swarm clears the
+model it set. It holds the model the agent runs when neither the swarm nor
+`HIVE_DEFAULT_MODEL` (agent.nix) names one. Nothing in the harness
+writes it. Path overridable via `HYPERHIVE_MODEL_FILE`. Survives
+destroy/recreate, gone on `--purge`.
 
 ### `/harness/paused` (per agent)
 
@@ -313,7 +313,7 @@ Under `/var/lib/hyperhive/agents/<name>/`:
     tables above.
   - `hyperhive-events.sqlite` — turn-loop event log.
   - `hyperhive-turn-stats.sqlite` — per-turn timing stats.
-  - `hyperhive-model` — single-line model name override file.
+  - `hyperhive-model` — single-line model name file, read-only fallback.
 - `work/` — the agent's working space for git worktrees, build dirs
   and other large working data. Bind-mounted RW to
   `/agents/<name>/work` inside the container and owned by the agent

docs/swarm/inference.md

@@ -20,14 +20,15 @@ swarmctl agent inference clear iris
   agent's `availableModels` as the models its subagent `start` and
   `continue` calls may name, read on each call
   ([`subagent.md`](../tools/subagent.md#which-models-a-subagent-may-run-on)).
-  The web UI's model picker doesn't use it.
 - `get` shows each field, naming the unset ones (or says the swarm sets
   nothing for the agent), and then the model and effort the agent reports
   running on, each with where it comes from.
 - `clear` removes every field; the agent goes back to its own values.
 
 The full flag reference is [`swarmctl-cli.md`](../tools/swarmctl-cli.md). The
-swarm UI's agents page edits the same settings; see [UI](ui.md).
+swarm UI's agents page edits the same settings; see [UI](ui.md). The
+swarm is the only place to change an agent's model at runtime: its web UI
+shows the model but has no picker and no `/model` command.
 
 ## What an agent runs on
 
@@ -47,11 +48,14 @@ Each running value names where it comes from:
 | ------------ | -------------------------------------------------------------------------- |
 | `swarm`      | the value set here                                                         |
 | `agent_nix`  | `services.hyperhive.agent.model` or `effortLevel` in the agent's agent.nix |
-| `local_file` | a `/model` or `/effort` pick in the agent's web UI                         |
+| `local_file` | an `/effort` pick in the agent's web UI, or a `hyperhive-model` file       |
 | `default`    | the harness's built-in default (`haiku`, `medium`)                         |
 
 When the agent starts without a swarm value, its agent.nix model wins over
-its `/model` pick, and its `/effort` pick wins over its agent.nix effort.
+a `hyperhive-model` file, and its `/effort` pick wins over its agent.nix
+effort. A `hyperhive-model` file comes from a runtime model pick the
+agent's web UI no longer offers; the agent still reads it but never writes
+it.
 
 The agent reports these whenever they change, and again once a minute.
 swarm-controller keeps only what it has received since it started, so for up
@@ -63,13 +67,13 @@ Each agent reads its settings every 10 seconds and switches on the next
 read: its next turn runs on the new model or effort, and its web UI badge
 shows it. A turn already running keeps what it started with.
 
-- **Its own value is the one it runs without the swarm**, from a `/model`
-  or `/effort` pick in its web UI or from its agent.nix. Setting a swarm
+- **Its own value is the one it runs without the swarm**: its agent.nix, an
+  `/effort` pick in its web UI, or a `hyperhive-model` file. Setting a swarm
   value doesn't overwrite it.
 - **Clearing a field** (or the whole key) puts the agent back on its own
   value on the next read.
-- **A `/model` or `/effort` pick while the swarm sets that field** changes
-  the agent's own value, but the swarm value comes back on the next read.
+- **An `/effort` pick while the swarm sets effort** changes the agent's own
+  value, but the swarm value comes back on the next read.
 - **After a restart**, the agent runs its own values until its first read
   of its settings succeeds.
 

docs/tools/swarmctl-cli.md

@@ -146,7 +146,7 @@ Queues and returns, the same way `agent create` does — watch the swarm UI's jo
 
 Show or change the model, effort and subagent models the swarm sets for an agent.
 
-A field the swarm sets wins over the agent's own value (from its `/model` or `/effort` pick or its agent.nix) from its next turn on; the agent reads its settings every ten seconds. A field the swarm doesn't set, or clears, leaves the agent on its own value.
+A field the swarm sets wins over the agent's own value (its agent.nix, its `/effort` pick, or a `hyperhive-model` file) from its next turn on; the agent reads its settings every ten seconds. A field the swarm doesn't set, or clears, leaves the agent on its own value.
 
 **Usage:** `swarmctl agent inference <COMMAND>`
 

docs/turn-loop/claude-invocation.md

@@ -50,13 +50,12 @@ live, which managed scope would otherwise lock.
 The harness reads `<name>` from `Bus::model()` on each turn.
 `services.hyperhive.agent.model` in the agent's `agent.nix` sets the initial
 default (NixOS option; propagates via `HIVE_DEFAULT_MODEL` env var; falls
-back to `"haiku"` if unset). The operator can flip it at runtime
-with `/model <name>` in the web terminal — the next turn picks it
-up. The harness persists the choice to `/harness/hyperhive-model` so it
-survives restart; override path: `HYPERHIVE_MODEL_FILE` env var
-for tests. A model or effort the swarm sets for the agent replaces the
-`Bus` value, and the harness doesn't persist it; clearing it goes back to
-the persisted or nix value → [`swarm/inference.md`](../swarm/inference.md).
+back to an existing `/harness/hyperhive-model` file, then `"haiku"`, if
+unset). The swarm changes the model at runtime, not the web
+terminal: a model or effort the swarm sets for the agent replaces the
+`Bus` value from the next turn, and the harness doesn't persist it;
+clearing it goes back to the local value →
+[`swarm/inference.md`](../swarm/inference.md).
 
 `harness_state::context_window_tokens(model)` looks up
 context-window size per-model. Resolution order (first

docs/web-ui/agent.md

@@ -47,15 +47,18 @@ at a given viewport width. Two columns:
     `◌ needs login` / `◌ logging in` / `○ offline` / `… connecting`.
   - **State badge**: `💤 idle` / `🧠 thinking` / `📦 compacting` /
     `○ offline` / `… booting` + age suffix.
-  - **Model badge** (`model · <name> ▾`): a real picker — selecting it opens
-    a `Dropdown` of `state.available_models`, selecting one POSTs
-    `/api/model` immediately (same endpoint the `/model <name>` slash
-    command uses). A header badge: the control and its display sit
-    together.
-  - **Effort badge** (`effort · <level> ▾`): same shape, `/api/effort`,
-    shown when `state.available_efforts` is non-empty.
-  - On an ACP agent both pickers list what its session offers (its
-    `model` and `thought_level` config options), and are empty until the
+  - **Model badge** (`model · <name>`): display only. Its tooltip says where
+    the model comes from (`state.model_source`: set on the swarm, agent.nix,
+    an existing `hyperhive-model` file, or the built-in default) and what the
+    last turn resolved it to. The model is set on the swarm: the swarm UI's
+    agents page, or `swarmctl agent inference set`
+    ([`inference.md`](../swarm/inference.md)).
+  - **Effort badge** (`effort · <level> ▾`): a real picker — selecting it
+    opens a `Dropdown` of `state.available_efforts` and POSTs `/api/effort`
+    immediately. Shown when `state.available_efforts` is non-empty.
+  - On an ACP agent the model badge shows the session's own model when it
+    doesn't offer the requested one, and the effort picker lists the levels
+    its session offers (its `thought_level` config option), empty until the
     first turn has attached a session. The effort picker is hidden when the
     model offers no effort levels, and while a newly picked model waits for
     the next turn, since the levels come with the model.
@@ -82,8 +85,8 @@ at a given viewport width. Two columns:
     (`GET /api/state`'s `links` field) also feeds
     `DashboardState.links` for the dashboard card's icon strip —
     `agent_links()` in hive-agent is the single source of truth for
-    both. The dashboard link lives in this 🔗 popover; the model/effort
-    pickers are real badges above; and `/new-session` / `/logout` are
+    both. The dashboard link lives in this 🔗 popover; the effort picker
+    is a real badge above; and `/new-session` / `/logout` are
     typed slash commands with their own type-twice confirm (see
     below).
   - `/cancel` (slash command, below) is the only cancel-turn path; the
@@ -234,10 +237,6 @@ Slash commands today:
   runs the `/compact` at the next turn boundary (end of the in-flight
   turn, or `turn::run_pending_compact` when idle); output streams into
   the live panel. Works mid-turn, not only when idle.
-- `/model <name>` — `POST /api/model` flipping `Bus::set_model`.
-  Takes effect on the next turn; persisted to
-  `/state/hyperhive-model` so the override survives harness
-  restart / rebuild.
 - `/effort <level>` — `POST /api/effort` setting the claude effort
   level (`low` / `medium` / `high` / `xhigh` / `max`). Takes effect on the next
   turn. `StatusChips`' effort badge calls the same endpoint; both stay
@@ -276,17 +275,15 @@ shaped).
   turn — only the stdin payload differs). Flips state to
   `Compacting` via `Bus::set_state`, which emits
   `TurnStateChanged`.
-- `POST /api/model` (`model=<name>`) — switch the model for
-  future turns. `Bus::set_model` emits `ModelChanged`.
 - `POST /api/effort` (`effort=<level>`) — switch the claude
   effort level for future sessions. Validated server-side against
   `EFFORT_LEVELS` (`low`/`medium`/`high`/`xhigh`/`max`) — unknown values are
   rejected rather than forwarded to `claude --effort`. Persists via
   `Bus::set_effort`, which emits `EffortChanged`. Applies on the next
   session start (no mid-session swap).
-- On an ACP agent, `/api/model` and `/api/effort` accept only values the
-  session offers, and the runtime sets them with `session/set_config_option`
-  before the next prompt.
+- On an ACP agent, `/api/effort` accepts only values the session offers,
+  and the runtime sets the level with `session/set_config_option` before
+  the next prompt.
 - `POST /api/new-session` — arm a one-shot for the next turn to
   drop `--continue`. Emits a `LiveEvent::Note`.
 - `POST /api/logout` — three-step teardown that re-uses the
@@ -320,7 +317,7 @@ shaped).
   the frontend (`useAgentState.ts`) on page load and, on a poll, while
   `status === 'needs_login_in_progress'`. Includes `turn_state`,
   `context_window_tokens`, `qualified_label`,
-  `available_models`, `effort`, `available_efforts`, `links`, and
+  `model`, `model_source`, `effort`, `available_efforts`, `links`, and
   other fields described inline throughout this document. All
   subsequent state updates arrive via SSE.
 - `GET /api/dashboard-state` — lean snapshot of agent-owned fields
@@ -392,7 +389,8 @@ Bus events (new vocabulary on `/events/stream`):
   `needs_login_idle` / `needs_login_in_progress`. Drives the
   alive-badge. The harness sets `rate_limited` when it detects a
   429 response and clears it when the retry sleep expires.
-- `model_changed { model }` — drives the model chip.
+- `model_changed { model }` — drives the model chip. The harness emits it
+  when it applies or clears a swarm value.
 - `effort_changed { effort }` — drives the effort picker chip.
   Emitted from `Bus::set_effort` on `POST /api/effort`; applies on
   the next session start.