feat(tui): opt-in auto-resume of the most recent session (#17130)

* feat(tui): opt-in auto-resume of the most recent session

`hermes --tui` always forges a fresh session at startup unless the user
sets `HERMES_TUI_RESUME=<id>`.  Disconnects, terminal-window crashes,
and accidental Ctrl+D therefore lose every piece of in-flight context
even though `state.db` still has the full history a `/resume` away.

Add an opt-in path that mirrors classic CLI's `hermes -c` muscle
memory: when `display.tui_auto_resume_recent: true` is set in
`~/.hermes/config.yaml`, the TUI looks up the most recent human-facing
session and resumes it instead of starting fresh.  Default off so
existing users aren't surprised; explicit `HERMES_TUI_RESUME` always
wins.

Wires:

* New `session.most_recent` JSON-RPC in `tui_gateway/server.py` that
  returns the first non-`tool` row from `list_sessions_rich`, or
  `{"session_id": null}` when none.  Uses the same deny-list as
  `session.list` so sub-agent rows can't sneak in.
* `createGatewayEventHandler.handleReady` re-ordered: explicit
  `STARTUP_RESUME_ID` first (unchanged), then conditional auto-resume
  via `config.get full → display.tui_auto_resume_recent`, then the
  legacy `newSession()` fallback.  Failures of either RPC fall back
  to `newSession()` so the path is always finite.
* Default `display.tui_auto_resume_recent: False` added to
  `DEFAULT_CONFIG` in `hermes_cli/config.py` (no `_config_version`
  bump per AGENTS.md — deep-merge handles the additive key).

Tests:

* 4 new vitest cases in `createGatewayEventHandler.test.ts` cover
  every gate-and-fallback combination (env wins, config off, config
  on with hit, config on with miss).
* 3 new pytest cases for `session.most_recent` (denied row skip,
  tool-only → null, db-unavailable → null).

Validation:
  scripts/run_tests.sh tests/test_tui_gateway_server.py — 93/93.
  cd ui-tui && npm run type-check — clean; npm test --run — 393/393.

* review(copilot): fold session.most_recent errors into null + extend ConfigDisplayConfig

* review(copilot): cover RPC-rejection fallbacks in auto-resume tests

ui-tui/src/__tests__/createGatewayEventHandler.test.ts

@@ -458,6 +458,152 @@ describe('createGatewayEventHandler', () => {
     })
   })
 
+  it('on gateway.ready with no STARTUP_RESUME_ID and auto_resume off, forges a new session', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = ''
+    ctx.gateway.rpc = vi.fn(async (method: string) => {
+      if (method === 'config.get') {
+        return { config: { display: { tui_auto_resume_recent: false } } }
+      }
+
+      return null
+    })
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(newSession).toHaveBeenCalled())
+    expect(resumeById).not.toHaveBeenCalled()
+  })
+
+  it('on gateway.ready with auto_resume on and a recent session, resumes it', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = ''
+    ctx.gateway.rpc = vi.fn(async (method: string) => {
+      if (method === 'config.get') {
+        return { config: { display: { tui_auto_resume_recent: true } } }
+      }
+
+      if (method === 'session.most_recent') {
+        return { session_id: 'sess-most-recent' }
+      }
+
+      return null
+    })
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(resumeById).toHaveBeenCalledWith('sess-most-recent'))
+    expect(newSession).not.toHaveBeenCalled()
+  })
+
+  it('on gateway.ready with auto_resume on but no eligible session, falls back to new', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = ''
+    ctx.gateway.rpc = vi.fn(async (method: string) => {
+      if (method === 'config.get') {
+        return { config: { display: { tui_auto_resume_recent: true } } }
+      }
+
+      if (method === 'session.most_recent') {
+        return { session_id: null }
+      }
+
+      return null
+    })
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(newSession).toHaveBeenCalled())
+    expect(resumeById).not.toHaveBeenCalled()
+  })
+
+  it('on gateway.ready when config.get rejects, falls back to new session', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = ''
+    ctx.gateway.rpc = vi.fn(async (method: string) => {
+      if (method === 'config.get') {
+        throw new Error('gateway timeout')
+      }
+
+      return null
+    })
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(newSession).toHaveBeenCalled())
+    expect(resumeById).not.toHaveBeenCalled()
+  })
+
+  it('on gateway.ready when session.most_recent rejects, falls back to new session', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = ''
+    ctx.gateway.rpc = vi.fn(async (method: string) => {
+      if (method === 'config.get') {
+        return { config: { display: { tui_auto_resume_recent: true } } }
+      }
+
+      if (method === 'session.most_recent') {
+        throw new Error('db locked')
+      }
+
+      return null
+    })
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(newSession).toHaveBeenCalled())
+    expect(resumeById).not.toHaveBeenCalled()
+  })
+
+  it('on gateway.ready with STARTUP_RESUME_ID set, the env wins over config auto_resume', async () => {
+    const appended: Msg[] = []
+    const newSession = vi.fn()
+    const resumeById = vi.fn()
+    const ctx = buildCtx(appended)
+
+    ctx.session.newSession = newSession
+    ctx.session.resumeById = resumeById
+    ctx.session.STARTUP_RESUME_ID = 'env-explicit'
+    ctx.gateway.rpc = vi.fn(async () => ({
+      config: { display: { tui_auto_resume_recent: true } }
+    }))
+
+    createGatewayEventHandler(ctx)({ payload: {}, type: 'gateway.ready' } as any)
+
+    await vi.waitFor(() => expect(resumeById).toHaveBeenCalledWith('env-explicit'))
+    expect(newSession).not.toHaveBeenCalled()
+  })
+
   it('keeps gateway noise informational and approval out of Activity', async () => {
     const appended: Msg[] = []
     const ctx = buildCtx(appended)