fix(local-model): a chip that was only looked at never hides "Start a session"

Selecting a chip stored it for the device at once. Someone who clicked
"DeepSeek" (Needs setup) or "Pi" (Not installed) just to see what it
says then got a window that reopened on that chip: "Install Pi", or no
main button at all, with "Start a session" out of sight.

The device now remembers the agent a session was STARTED with, an
opening of the window selects it only while it can be started, and a
selection made in one opening does not carry into the next. Otherwise
the server's default agent is selected, as before.

Also: a real-browser test for the chips (they wrap inside the window at
1440, 390 and 320 px, the install command included, one tab stop), and
one sentence in the API reference: a readiness mark says the composer is
there, not that nothing else is (DeepSeek Harness's setup guide draws
the same glyph).

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

docs/api-reference.md

@@ -1796,7 +1796,7 @@ A probe that fails is an answer, not an error: a server that is not on macOS, or
   - `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.
-  - `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).
+  - `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. A mark says the composer is there, not that nothing else is: DeepSeek Harness with dsh-TUI 0.19 opens a setup guide whose cursor is its `❯` too until a person has finished it once, so a script reads the pane after the 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: