feat(web): move the agent plane behind per-session presets

The Web overlay disables base's 32 agent-plane rows and mounts the preset
roster instead, so each session composes its own tools and prompt rather than
sharing one process-wide set. The TUI keeps base unchanged: it is single-session
and composing its agent process-wide is correct there.

`roots` is patched in by AppCLIEntry, like `distIndex`: the shipped presets sit
beside the composition that names them and the user's live under the Harness
home, neither of which a config author chooses.

A session's preset is fixed at creation. Naming a different one for an existing
identity is `agent-preset-conflict` rather than a switch, because that
session's history was produced under the first preset's tools. The guard sits
after `await creation`, beside the cwd check, so it covers every path that
yields a live agent — freshly created, adopted live, resumed, or recovered by
the concurrent-creation catch. A request naming no preset adopts the session as
it is, keeping reconnect and retry ordinary.

Two bugs the real-composition test caught, both invisible to unit tests:

`PresetTree` now refuses to write. The Loader persists a tree whose plugin
self-disposed, and tearing an agent down disposes its whole subtree — inherited,
that rewrote the shipped composition, truncating a 241-line preset to `[]` the
first time a session ended.

`dsh-tool-skill` compared against a lookup of its own name in the global layer,
so it threw inside any preset: `register()` files into the calling context's
scope. It now compares against the definition it registered, which is what the
identity check meant all along.

The `standard` catalog is asserted exactly, not spot-checked: a row that
registers into the wrong layer mounts cleanly and simply contributes nothing, so
an omission is this design's quietest failure. It matches the shipped TUI
catalog plus `glob`/`grep`, the pair that composition documents as
ripgrep-dependent.

Re-records `cordis-inspect-jsdoc`, whose rendered `SessionHeader` gains the
`agentPreset` field. `fs-glob-sampling` fails identically on pristine master
and is untouched here.

The browser e2e scaffold gains the roster fact AppCLIEntry supplies. `roots` is
resolved and patched in by the CLI entry, like `distIndex` on the webserver row,
and this lane boots the shipped tree without that entry — so it has to supply
the same fact or the roster resolves nothing and every session in the lane
composes an agent with no tools, no persona, and no token meter. Only the
shipped root: a developer's own `~/.dsh/.agent-presets` must not decide a golden. The
`cordis:group` builtin comes with it, exactly as `boot()` registers it, because
a preset resolving package names from its own directory cannot reach
`@cordisjs/plugin-group` by name.

The lane stays red through this layer and the next four for the reason stated
above — the api-proxy injects `subagents`, `workspace`, and `tools`, so
`api-gateway` cannot activate and the browser has no `/api` at all. It goes
green again in the layer that returns those registries to the host plane; this
change is what makes that layer's fix sufficient rather than partial.

packages/bundle/web-app/cordis.patch.yml

@@ -189,3 +189,122 @@
 
     - id: ui-trajectory
       name: '@deepseek-ai/dsh-client-ui-trajectory'
+
+# ── the agent plane moves behind agent presets ─────────────────────────────
+#
+# Every row below composes what ONE agent contributes to the host registries:
+# its tools, its prompt sections, its delegation backends. The base keeps them
+# for the TUI, which is single-session and composes its agent process-wide; the
+# Web surface disables them here and lets each session mount a preset instead.
+#
+# Disabling rather than deleting is deliberate: the base is shared, and a row
+# absent from a surface overlay would silently reappear the day someone reorders
+# the composition.
+
+- id: tool-bash
+  disabled: true
+
+- id: tool-tasks
+  disabled: true
+
+- id: tasks
+  disabled: true
+
+- id: tool-fs
+  disabled: true
+
+- id: tool-fs-search
+  disabled: true
+
+- id: tool-str-replace-editor
+  disabled: true
+
+- id: skill
+  disabled: true
+
+- id: skill-local
+  disabled: true
+
+- id: tool-skill
+  disabled: true
+
+- id: goal
+  disabled: true
+
+- id: goal-session
+  disabled: true
+
+- id: command-goal
+  disabled: true
+
+- id: tool-goal
+  disabled: true
+
+- id: plan-mode
+  disabled: true
+
+- id: token-meter
+  disabled: true
+
+- id: compact-basic
+  disabled: true
+
+- id: command-compact
+  disabled: true
+
+- id: tool-result-prune
+  disabled: true
+
+- id: subagent
+  disabled: true
+
+- id: subagent-spawn
+  disabled: true
+
+- id: subagent-fork
+  disabled: true
+
+- id: tool-subagent-control
+  disabled: true
+
+- id: tool-subagent-list-agents
+  disabled: true
+
+- id: tool-subagent
+  disabled: true
+
+- id: tool-subagent-fork
+  disabled: true
+
+- id: tool-subagent-report
+  disabled: true
+
+- id: workflow-workerthread
+  disabled: true
+
+- id: tool-workflow
+  disabled: true
+
+- id: tool-ralph
+  disabled: true
+
+- id: workspace-context
+  disabled: true
+
+- id: tool-todo
+  disabled: true
+
+- id: tool-web
+  disabled: true
+
+# The preset roster. `.system` ships with the deployment and is read-only;
+# `$DSH_HOME/.agent-presets` is where a person — or an agent — authors their own, and
+# carries the same trust as shell access because a preset IS a composition.
+# `roots` is an assembly fact, not user config: the shipped preset directory
+# ships beside this file, so AppCLIEntry resolves it and patches it in — the
+# same treatment `distIndex` gets on the webserver row.
+- insert:
+    - id: agent-presets
+      name: '@deepseek-ai/dsh-agent-presets'
+      config:
+        default: standard