docs(local-model): the coding agents of a model, what each was measured with, and the agent install

- docs/local-models.md: the four agents with their first request, whether
  the window installs them and what was seen where (a real model, a
  scripted endpoint, Linux, not the pinned runtime); what differs for Pi
  and for DeepSeek Harness; installing one more agent beside a model.
- docs/api-reference.md: `POST /api/local-model/agent`, `install.harnesses`,
  the `install-agent` action, and `install.cli` as the default agent.
- docs/architecture-invariants.md, CLAUDE.md, src/web/CLAUDE.md: the
  rules: the agent is chosen per session, the agent install is not a
  job, a launcher is never installable, a readiness mark is a measured
  one, and the window's one builder for the agent chips.
- docs/custom-model-endpoints.md: Pi's context window.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

docs/api-reference.md

@@ -1716,7 +1716,7 @@ Only replies from `allowedUserIds`, in `guildId`, inside a thread the bridge cre
 
 ## Local model
 
-`GET /api/local-model` looks at the machine the server runs on and says which local coding model fits it, with which agent CLI, where an install of one stands and which models are on the machine. Seven verbs install a model (a first one, or another one beside it), switch to a model that is already there, pause and continue a job, stop and start the model runtime, delete one model, and remove everything again. It covers Apple silicon macOS only; anywhere else the GET is still a `200`, with verdict `none`, and nothing can be installed. How it works: [local-models.md](local-models.md).
+`GET /api/local-model` looks at the machine the server runs on and says which local coding model fits it, with which agent CLI, where an install of one stands and which models are on the machine. Eight verbs install a model (a first one, or another one beside it), switch to a model that is already there, pause and continue a job, stop and start the model runtime, delete one model, install one more agent CLI beside an installed model, and remove everything again. It covers Apple silicon macOS only; anywhere else the GET is still a `200`, with verdict `none`, and nothing can be installed. How it works: [local-models.md](local-models.md).
 
 **Experimental.** These routes and their payloads are labeled experimental: the fields below, the states, the error codes and the sentences may change or go in a MINOR or PATCH release (see [versioning-policy.md](versioning-policy.md), "What SemVer does NOT cover", item 3). Do not build on their shape yet.
 
@@ -1732,6 +1732,7 @@ Every route is admin only in multi-user mode (`403 FORBIDDEN`, answered before a
 | `POST`   | `/api/local-model/runtime` | `{ action: "start" \| "stop", newPort? }`        | `stop` stops the runtime and keeps it from starting at the next boot; `start` undoes that. `newPort: true` with `start` chooses another port and moves the saved endpoint to it. `409`: `job-running`, `wrong-state` (nothing is installed), `sessions-open` (`stop` or `newPort` while live sessions use the model: their agents keep calling the address they were started with). |
 | `DELETE` | `/api/local-model`         | `{ removeModel? }` (may be absent)               | Stops the runtime, removes the saved endpoint, restores the settings flag when this feature switched it on and no other endpoint is saved, deletes the runtime; the downloaded models (all of them) only with `removeModel: true`. With nothing installed it is what deletes the models an earlier Remove kept. `409`: `job-running`, `sessions-open`. |
 | `DELETE` | `/api/local-model/models`  | `{ modelId }`                                    | Deletes ONE model from the store, through the runtime. `modelId` is a model name (`name:tag`) of `install.library` whose `actions` list `delete`, never a path. `400 INVALID_INPUT` for a name that is not on this machine. `409`: `job-running`, `wrong-state` (nothing is installed), `model-active` (the model of the installation or of the current job), `runtime-not-running`. `500 OPERATION_FAILED` when the runtime did not delete it. |
+| `POST`   | `/api/local-model/agent`   | `{ cli }`                                        | Installs one more agent CLI beside an installed model and answers at once; the installer runs on in the server and `install.harnesses` says how it stands. `cli` is a row of `install.harnesses` whose `actions` list `install`; the server runs that row's `installCommand`, the release's own stock command, never text from the request. It is not a job: `install.state` stays `installed` whatever the installer does, sessions are not refused, and no live session is looked at. An agent that can already be started answers `200` with the view as it is. `400 INVALID_INPUT` for a CLI that is not a row of `install.harnesses`, or one that one command does not make startable (`setup-needed`). `409`: `job-running` (a job, or another agent install, is running), `wrong-state` (nothing is installed). |
 
 Every verb answers `{ success: true, data: <install> }` with the `install` object (below) as it is after the verb. A refusal the feature names is a `409` whose envelope also carries the conflict:
 
@@ -1786,16 +1787,17 @@ A probe that fails is an answer, not an error: a server that is not on macOS, or
   - `step` and `steps[]` (present with `installing`, `paused` and `failed`): the step the job is in or stopped in, and the steps of this job in order, out of `runtime`, `model`, `verify`, `agent`, `connect`. `agent` is absent from a job whose agent CLI was already installed. A switch (`POST .../use`) is the two steps `verify` and `connect`.
   - `progress` (while a download runs, and as it stood on a paused or failed job): `completedBytes`, `totalBytes`, `completedGb`, `totalGb`, and while it moves `bytesPerSecond`, `mbPerSecond` (whole decimal megabytes per second as text) and `secondsLeft`. During the `model` step both byte figures come from the download's own lines, not from the catalogue.
   - `error` (with `failed`; with `installed` only when something blocks a session): `{ code, message: { text, vars? }, next, nextModel?, detail? }`. `next` is the ONE action that helps: `retry` (`POST .../resume`), `other-port` (`POST .../resume` or `.../runtime` with `newPort: true`), `next-model` (choose again; `nextModel` is `{ modelId, modelLabel }` when the server knows one), `start` (`POST .../runtime`) or `remove` (`DELETE`). `detail` is raw text for the curious (an installer's last lines), not translated.
-  - `model` (`{ id, label }`), `cli`, `cliLabel`, `context`: the choice of the job or of the installation. `port`: the runtime's loopback port, once chosen.
+  - `model` (`{ id, label }`), `cli`, `cliLabel`, `context`: the choice of the job or of the installation. With `installed`, `cli` is the DEFAULT agent CLI, the one a client that names none starts: the agent of the installation while it can be started, else the first row of `harnesses` that can. `port`: the runtime's loopback port, once chosen.
   - `running`: the runtime Codeman started is alive right now. A runtime the person stopped is `running: false` with no `error`.
   - `loaded` (with `installed`): what the runtime reported when the job checked the loaded model: `context`, `memoryBytes`, `memoryGb`, `onGpu`.
-  - `endpointId` (with `installed`): the saved model endpoint a session is started on, with `cli`.
+  - `endpointId` (with `installed`): the saved model endpoint a session is started on, with `cli` or with any row of `harnesses` that offers `start-session`.
   - `developerTools`: `present`, `missing` (the Mac has no Xcode or Command Line Tools, so macOS will offer to install them the first time an agent runs `git` or `python3`) or `unknown`.
   - `runtime`: `{ version, installed, downloadBytes, downloadGb, unpackedGb }`. `downloadBytes` is `0` once the runtime is unpacked.
   - `folder`: the absolute folder everything of this feature is kept in.
   - `library[]`: the models on this machine, the model in use first. Empty with `idle` (no runtime is there to ask). Each row: `id` (the name the runtime lists, `name:tag`), `label`, `context?` (the context it was checked with), `sizeBytes?` and `sizeGb?` (its size on disk as the runtime reports it, else as recorded when it was checked), `active` (it is the model in use), `verified` (Codeman checked it), `status` and `actions[]`. `status` is `ready`, `changed` (checked, and the runtime now reports another digest under the name), `missing` (checked, and the runtime no longer lists it) or `unverified` (the runtime lists it and Codeman never checked it: a model an earlier Remove kept, the model of a job that has not passed its check, or one another program pulled through the runtime's port). `actions` is what the server accepts for THAT row right now, out of `use` and `delete`; `delete` needs the running runtime, and a name that is not a plain `name:tag` is listed with no action.
   - `store?`: `{ bytes, gb }`, what the model store takes on disk (the files of its blob folder, so shared layers count once and an interrupted download is included). Present in every state once it was measured; cached for about thirty seconds.
-  - `actions[]`: exactly what the server accepts right now, out of `install` (with `installed`: add another model), `cancel`, `resume`, `start`, `stop`, `remove` (with `idle` only while `store` holds something), `use` and `delete-model` (only while a row of `library` offers them) and `start-session` (not a route here: start a session on `endpointId`; offered only while the runtime runs and nothing blocks a session).
+  - `harnesses[]`: the agent CLIs a session on the model in use can be started with, the default one first, then by the catalogue's rank. The agent is chosen per session: a session is started with `mode` set to a row's `cli` and `customModel: { endpointId, modelId }`. Empty in every state but `installed`. Each row: `cli`, `cliLabel`, `default` (true on the row `install.cli` names), `status`, `installCommand?` (with `installable` and `installing`: the literal command `POST .../agent` runs), `slowFirstTurn?` (the first answer takes minutes), `readyMark?` (a literal without white space that the agent's composer draws once it takes input: what a script waits for on `GET /api/sessions/:id/wait-output` before it sends the first prompt; absent for an agent with no measured mark), `error?` (`{ message, detail? }`: the last install of this agent through `POST .../agent` failed; kept in memory only) and `actions[]` (`start-session`, `install`). `status` is `ready` (it can be started, the answer the Run menu gets), `installable` (not on this machine, and `POST .../agent` installs it), `installing` (that install is running; the model stays as it is) or `setup-needed` (not startable, and one command does not make it so: DeepSeek Harness without a terminal profile, or a command that needs an administrator; set it up from the Run menu or a terminal).
+  - `actions[]`: exactly what the server accepts right now, out of `install` (with `installed`: add another model), `cancel`, `resume`, `start`, `stop`, `remove` (with `idle` only while `store` holds something), `use` and `delete-model` (only while a row of `library` offers them), `install-agent` (only while a row of `harnesses` offers `install`) and `start-session` (not a route here: start a session on `endpointId`; offered only while the runtime runs, nothing blocks a session and, when `harnesses` is known, at least one agent CLI can be started).
 
 Error codes (`install.error.code`), each with one next step: