refactor(cli)!: one shared base config with per-surface overlays

`dsh` shipped two config trees that were 43 rows the same: apps/cli/cordis.yml
composed web as 74 flat rows, while the TUI booted examples/tui-agent/cordis.yml
whose single `@deepseek-ai/dsh-tui-demo` row mounted twelve plugins behind a
twenty-key pass-through Config. Neither file was what its location claimed —
apps/cli hardcoded the "example" as the product default and the "demo" bundle
was the application — and every capability change had to be made twice.

- apps/cli/base.cordis.yml holds the 43 shared rows; tui.cordis.yml and
  web.cordis.yml are patch lists stating only what differs per surface
- overlays apply as SIBLING patch lists at one include level, because include
  patches never cross an include boundary. Precedence: base < surface <
  (--config | personal ~/.dsh/config.yaml) < launcher flag/profile patches
- `--config` now applies an overlay INSTEAD OF the personal one, so a demo or
  test tree never inherits the user's route; new `--config-replace` boots a file
  as the entire tree (the old `--config` behaviour). Both survive /resume
- vendor/include: index each `insert`ed row as it is added so a later patch can
  configure or disable it. Upstream built the id index once before the patch
  loop, leaving every surface-only row — the whole TUI front door — silently
  unpatchable from user config. Logged as local modification 8
- session identity moves to dsh-agent-loop's CONFIGURED_AGENT_IDENTITIES_KEY;
  dsh-tui's MAIN_SESSION_ID_KEY is deleted (only the bundle read it)
- delete examples/tui-agent, examples/cordis-agent, packages/examples/tui-demo;
  TUI tests → apps/cli/tests, cordis e2e → packages/cordis/tool-cordis/tests,
  examples/code-mode survives as an overlay leaf
- `dsh web` gains --config, threaded into AppCLIEntry as an extra overlay

Three latent defects surfaced and are fixed here: the TUI captured the optional
sessionQuery service once at construction and could permanently disable /resume
when it won the mount race; the session-store root silently reverted to a
project-local ./.sessions; --config-replace was dropped by the resume handoff.

Verified by booting each tree through the real Loader (TUI 55 entries, web 75,
zero unsettled) rather than reading YAML. All eight terminal snapshots replay
byte-identically; 14/14 PTY smoke, 112/112 snapshots, 25/25 doc-sync, hygiene
and lint clean.

packages/core/agent-loop/src/index.ts

@@ -134,6 +134,15 @@ interface PreparedAgent {
 declare module 'cordis' {
   interface Context {
     agentLoop: AgentLoop
+    /**
+     * Launcher-owned exact session identities for configured agents, keyed by
+     * the agent's config `id` and set with `ctx.provide()` before any Loader
+     * entry mounts (see {@link CONFIGURED_AGENT_IDENTITIES_KEY}). A launcher
+     * owns identity because only it knows whether the session already exists,
+     * while the `cordis.yml` row keeps the model route as ordinary patchable
+     * config. An entry with no matching key keeps its configured identity.
+     */
+    configuredAgentIdentities?: ConfiguredAgentIdentities
   }
   interface Events {
     /**
@@ -151,6 +160,53 @@ declare module 'cordis' {
 
 export { DEFAULT_MAX_PARALLEL_TOOL_CALLS }
 
+/**
+ * One launcher-selected session identity for a configured agent. `resume`
+ * distinguishes rehydrating existing persisted history from creating the
+ * session fresh under that exact id, which the two config keys express as
+ * `resumeSessionId` and `sessionId`.
+ */
+export interface LauncherAgentIdentity {
+  /** Exact session id to create fresh or resume. */
+  id: SessionId
+  /** Resume existing persisted history instead of creating the session fresh. */
+  resume: boolean
+}
+
+/** Launcher-selected identities keyed by the configured agent's `id`. */
+export type ConfiguredAgentIdentities = Readonly<Record<string, LauncherAgentIdentity>>
+
+/**
+ * Context key a launcher sets before any Loader entry mounts
+ * (`ctx.provide(CONFIGURED_AGENT_IDENTITIES_KEY, identities)`) to fix
+ * configured agents' session identities without a config key, so an overlay
+ * repointing the row's model route cannot drop them.
+ */
+export const CONFIGURED_AGENT_IDENTITIES_KEY = 'configuredAgentIdentities'
+
+/**
+ * Apply launcher-owned identities over the configured agents, replacing both
+ * identity keys for every entry the launcher named so a config-supplied
+ * identity can never survive alongside a launcher-supplied one.
+ * @param agents - the configured agent entries.
+ * @param identities - launcher identities keyed by configured agent `id`, or `undefined`.
+ * @returns the entries with launcher-owned identities applied.
+ */
+function applyLauncherIdentities(
+  agents: Config['agents'],
+  identities: ConfiguredAgentIdentities | undefined,
+): Config['agents'] {
+  if (identities === undefined) return agents
+  return agents.map((agent) => {
+    const identity = identities[agent.id]
+    if (identity === undefined) return agent
+    const { sessionId: _sessionId, resumeSessionId: _resumeSessionId, ...rest } = agent
+    return identity.resume
+      ? { ...rest, resumeSessionId: identity.id }
+      : { ...rest, sessionId: identity.id }
+  })
+}
+
 /** Agent-loop plugin configuration. */
 export interface Config {
   /**
@@ -220,6 +276,7 @@ export class AgentLoop extends Service implements AgentFactory {
     super(ctx, 'agentLoop')
     this.config = {
       ...config,
+      agents: applyLauncherIdentities(config.agents, ctx.get(CONFIGURED_AGENT_IDENTITIES_KEY)),
       maxParallelToolCalls: resolveMaxParallelToolCalls(config.maxParallelToolCalls),
     }
     validateConfiguredAgents(this.config.agents)