feat(web): author agent presets from a settings page

A composition is a file, but "edit it on the filesystem" is not a browser
affordance. The roster gains `read`/`write`/`remove` beside `select`, and
the browser gains a settings section over them: the presets as rows, one
composition open in a YAML editor at a time, and per-row default, duplicate,
and delete.

All four authoring methods are loopback-pinned. A composition names the
plugins a session runs, so reading one is reconnaissance, writing one is
arbitrary capability, and selecting one can move a session onto a preset
that edits the live runtime. `agentPreset.list` deliberately stays ordinary
and now reports `authorable`, so a surface knows whether creating is
possible at all rather than offering a button whose save always fails.

Authoring starts by duplicating: a shipped preset opens read-only because
the deployment's copy is what a broken local one is compared against. Ids
are contained before they become directory names, and the text is parsed
with the loader's own schema, so a save cannot leave a file no session
could load.

Fixes a defect the real-composition test found: a preset written under the
user's home could never mount, because the loader resolves a row against the
composition's own directory and Node's `node_modules` walk from there never
reaches the installed harness. The mount now records the host base and sends
bare specifiers there, leaving relative paths resolving from the preset.

Also closes the coverage the earlier surfaces in this stack shipped without —
the General row, the composer seat, and the plugin halves now have tests.

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -96,6 +96,18 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
         signature: 'async mount(agentCtx: Context, id?: string): Promise<AgentPreset>',
         jsDoc: '/**\n * Compose one agent from a preset, installing it under that agent alone.\n *\n * Call from the agent factory\'s `setup(agentCtx)`; a rejection there rolls\n * the agent creation back, so a broken preset never yields a half-composed\n * session.\n * @param agentCtx - the agent\'s scope context.\n * @param id - the preset id, or `undefined` for {@link defaultId}.\n * @returns the preset that was mounted, for the caller to record.\n * @throws when the preset is unknown or its composition is unusable.\n */',
       },
+      {
+        signature: 'async read(id: string): Promise<string>',
+        jsDoc: '/**\n * Read one profile\'s composition text.\n * @param id - the profile id.\n * @returns the composition exactly as stored.\n * @throws when no configured root supplies that id.\n */',
+      },
+      {
+        signature: 'async write(id: string, content: string): Promise<void>',
+        jsDoc: '/**\n * Create or replace a locally authored profile.\n *\n * The text is shape-checked before it lands, so a save cannot leave a file no\n * session could load; it is NOT mounted, so a composition that parses but\n * names a missing plugin still fails at the next session that selects it.\n * @param id - the profile id, which becomes its directory name.\n * @param content - the composition text.\n * @throws when the id is unusable, the text is not an entry list, or the\n * deployment configures no writable root.\n */',
+      },
+      {
+        signature: 'async remove(id: string): Promise<void>',
+        jsDoc: '/**\n * Delete a locally authored profile.\n * @param id - the profile id.\n * @throws when the profile is unknown or ships with the deployment.\n */',
+      },
       {
         signature: 'serviceFor<K extends string & keyof Context>(agent: { ctx: Context }, name: K): Context[K] | undefined',
         jsDoc: '/**\n * One agent\'s instance of a service its preset mounted.\n *\n * A preset publishes services behind `isolate` realms, which are invisible\n * outside the group that declares them — including to the host. This is how a\n * caller holding the agent reads one anyway: a request that is ABOUT a\n * session but arrives from outside it, which is every browser RPC.\n *\n * Read addressing only. A host row that `inject`s a service cannot use this,\n * because injection resolves before any session exists and has no agent to\n * key by; such a service belongs on the host plane instead.\n * @param agent - the agent whose composition to look inside.\n * @param name - the service name as the preset\'s rows resolve it.\n * @returns the agent\'s instance, or undefined when its preset mounts none.\n */',