fix(tui): route /save through session.save JSON-RPC

The cherry-picked approach serialized the UI-shaped transcript on the Node
side, producing a third JSON format alongside cli.py save_conversation and
tui_gateway session.save. Simpler to call the existing session.save method,
which already writes the canonical agent history (raw OpenAI messages +
model) to an absolute-path file.

- /save still short-circuits before the slash worker
- Empty transcript -> 'no conversation yet'
- No active session -> 'no active session - nothing to save'
- Otherwise: rpc('session.save', {session_id}) and echo back the file path
- Tests updated to assert RPC contract; new test covers the no-sid case

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

@@ -1,10 +1,8 @@
-import { existsSync, readFileSync, unlinkSync } from 'node:fs'
-
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { createSlashHandler } from '../app/createSlashHandler.js'
 import { getOverlayState, resetOverlayState } from '../app/overlayStore.js'
-import { getUiState, resetUiState } from '../app/uiStore.js'
+import { getUiState, patchUiState, resetUiState } from '../app/uiStore.js'
 
 describe('createSlashHandler', () => {
   beforeEach(() => {
@@ -290,57 +288,63 @@ describe('createSlashHandler', () => {
     expect(ctx.transcript.sys).toHaveBeenCalledWith('no conversation yet')
   })
 
-  it('/save writes the current TUI transcript without using the slash worker', () => {
-    vi.useFakeTimers()
-    vi.setSystemTime(new Date(2026, 3, 25, 15, 4, 5))
-    const filename = 'hermes_conversation_20260425_150405.json'
+  it('/save forwards to session.save RPC and reports the returned file', async () => {
+    patchUiState({ sid: 'sid-abc' })
 
-    try {
-      if (existsSync(filename)) {
-        unlinkSync(filename)
+    const rpc = vi.fn(() => Promise.resolve({ file: '/tmp/hermes_conversation_test.json' }))
+
+    const ctx = buildCtx({
+      gateway: { ...buildGateway(), rpc },
+      local: {
+        ...buildLocal(),
+        getHistoryItems: vi.fn(() => [
+          { role: 'system', text: 'intro' },
+          { role: 'user', text: 'hello' },
+          { role: 'assistant', text: 'hi there' }
+        ])
       }
-
-      const ctx = buildCtx({
-        local: {
-          ...buildLocal(),
-          getHistoryItems: vi.fn(() => [
-            { role: 'system', text: 'intro' },
-            { role: 'user', text: 'hello' },
-            { role: 'assistant', text: 'hi there', tools: ['read_file'] },
-            { role: 'tool', text: 'tool output' }
-          ])
-        }
-      })
-
-      createSlashHandler(ctx)('/save')
-
-      expect(ctx.gateway.gw.request).not.toHaveBeenCalled()
-      expect(ctx.transcript.sys).toHaveBeenCalledWith(`conversation saved to: ${filename}`)
-
-      const saved = JSON.parse(readFileSync(filename, 'utf8'))
-
-      expect(saved.messages).toEqual([
-        { role: 'user', text: 'hello' },
-        { role: 'assistant', text: 'hi there', tools: ['read_file'] },
-        { role: 'tool', text: 'tool output' }
-      ])
-    } finally {
-      if (existsSync(filename)) {
-        unlinkSync(filename)
-      }
-
-      vi.useRealTimers()
-    }
-  })
-
-  it('/save reports empty state without touching the slash worker', () => {
-    const ctx = buildCtx()
+    })
 
     createSlashHandler(ctx)('/save')
 
     expect(ctx.gateway.gw.request).not.toHaveBeenCalled()
+    expect(rpc).toHaveBeenCalledWith('session.save', { session_id: 'sid-abc' })
+
+    await vi.waitFor(() => {
+      expect(ctx.transcript.sys).toHaveBeenCalledWith(
+        'conversation saved to: /tmp/hermes_conversation_test.json'
+      )
+    })
+  })
+
+  it('/save reports empty state without calling the RPC or slash worker', () => {
+    const rpc = vi.fn(() => Promise.resolve({}))
+    const ctx = buildCtx({ gateway: { ...buildGateway(), rpc } })
+
+    createSlashHandler(ctx)('/save')
+
+    expect(ctx.gateway.gw.request).not.toHaveBeenCalled()
+    expect(rpc).not.toHaveBeenCalled()
     expect(ctx.transcript.sys).toHaveBeenCalledWith('no conversation yet')
   })
+
+  it('/save without an active session tells the user instead of hitting the RPC', () => {
+    // sid stays null (default) but there IS visible conversation
+    const rpc = vi.fn(() => Promise.resolve({}))
+
+    const ctx = buildCtx({
+      gateway: { ...buildGateway(), rpc },
+      local: {
+        ...buildLocal(),
+        getHistoryItems: vi.fn(() => [{ role: 'user', text: 'hello' }])
+      }
+    })
+
+    createSlashHandler(ctx)('/save')
+
+    expect(rpc).not.toHaveBeenCalled()
+    expect(ctx.transcript.sys).toHaveBeenCalledWith('no active session — nothing to save')
+  })
 })
 
 const buildCtx = (overrides: Partial<Ctx> = {}): Ctx => ({