fix(web): compose a forked session, and give the shell realm its provider

Two consequences of moving the agent plane behind presets, both invisible
until the host plane stopped carrying model-facing rows.

`sessions.fork` built its child with a bare `installTarget` and a `meta`
without `agentPreset`. That was harmless while every tool sat in the host
plane — the child inherited them for free. It now comes up with an EMPTY
tool set. The child composes the parent's preset instead, for the same
reason a resumed session keeps its own: the seeded history was produced
under those tools.

`bashEnv` lives in its own `dsh-bash-env` row rather than inside
`tool-bash`, so a preset that isolates the realm must compose the provider
beside its consumer; the host row is disabled here like every other
model-facing one. Nothing outside the agent plane injects `bashEnv`, so it
stays per-session.

apps/cli/config/agent-presets/core-web/agent.cordis.yml

@@ -22,6 +22,11 @@
   isolate:
     bashEnv: true
   config:
+    # The registry and its consumer share the realm: a consumer left outside
+    # would resolve the host's `bashEnv`, which this plane no longer provides.
+    - id: bash-env
+      name: '@deepseek-ai/dsh-bash-env'
+
     - id: tool-bash
       name: '@deepseek-ai/dsh-tool-bash'
 

apps/cli/config/agent-presets/standard/agent.cordis.yml

@@ -40,6 +40,11 @@
   isolate:
     bashEnv: true
   config:
+    # The registry and its consumer share the realm: a consumer left outside
+    # would resolve the host's `bashEnv`, which this plane no longer provides.
+    - id: bash-env
+      name: '@deepseek-ai/dsh-bash-env'
+
     - id: tool-bash
       name: '@deepseek-ai/dsh-tool-bash'