feat: add session export with full and compressed modes (#507)

Add export functionality that allows users to download session data
as JSON or plain text, with optional LLM-based context compression
for long conversations. Includes UI controls in chat panel, session
list, and history view, plus i18n strings for all 8 locales.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

tests/server/sessions-controller.test.ts

@@ -11,6 +11,7 @@ const getGroupChatServerMock = vi.fn()
 const getLocalUsageStatsMock = vi.fn()
 const getActiveProfileNameMock = vi.fn()
 const loggerWarnMock = vi.fn()
+const getCompressionSnapshotMock = vi.fn()
 
 vi.mock('../../packages/server/src/db/hermes/conversations-db', () => ({
   listConversationSummariesFromDb: listConversationSummariesFromDbMock,
@@ -67,6 +68,25 @@ vi.mock('../../packages/server/src/services/hermes/hermes-profile', () => ({
   getActiveProfileName: getActiveProfileNameMock,
 }))
 
+vi.mock('../../packages/server/src/db/hermes/compression-snapshot', () => ({
+  getCompressionSnapshot: getCompressionSnapshotMock,
+}))
+
+vi.mock('../../packages/server/src/lib/context-compressor/export-compressor', () => ({
+  ExportCompressor: class {
+    async compress(messages: any[]) {
+      return {
+        messages,
+        meta: { totalMessages: messages.length, compressed: true, llmCompressed: true, summaryTokenEstimate: 100, verbatimCount: 0, compressedStartIndex: -1 },
+      }
+    }
+  },
+}))
+
+vi.mock('../../packages/server/src/services/gateway-bootstrap', () => ({
+  getGatewayManagerInstance: () => null,
+}))
+
 describe('session conversations controller', () => {
   beforeEach(() => {
     vi.resetModules()
@@ -83,6 +103,7 @@ describe('session conversations controller', () => {
     getActiveProfileNameMock.mockReset()
     getActiveProfileNameMock.mockReturnValue('default')
     loggerWarnMock.mockReset()
+    getCompressionSnapshotMock.mockReset()
   })
 
   it('prefers the DB-backed conversations summary path', async () => {
@@ -198,4 +219,76 @@ describe('session conversations controller', () => {
       cost: 0.02,
     })
   })
+
+  describe('exportSession', () => {
+    it('returns session as JSON download with correct headers (full mode)', async () => {
+      const sessionData = { id: 'abc-123', title: 'Test Session', messages: [{ id: 1, role: 'user', content: 'hello' }] }
+      getSessionDetailFromDbMock.mockResolvedValue(sessionData)
+
+      const mod = await import('../../packages/server/src/controllers/hermes/sessions')
+      const setMock = vi.fn()
+      const ctx: any = { params: { id: 'abc-123' }, query: {}, set: setMock, body: null }
+
+      await mod.exportSession(ctx)
+
+      expect(getSessionDetailFromDbMock).toHaveBeenCalledWith('abc-123')
+      expect(setMock).toHaveBeenCalledWith('Content-Disposition', expect.stringContaining('abc-123'))
+      expect(setMock).toHaveBeenCalledWith('Content-Type', 'application/json')
+      expect(ctx.status).toBeUndefined()
+      expect(JSON.parse(ctx.body)).toMatchObject({ id: 'abc-123', title: 'Test Session' })
+    })
+
+    it('returns full TXT export', async () => {
+      const sessionData = {
+        id: 'txt-123',
+        title: 'Text Export',
+        messages: [
+          { id: 1, role: 'user', content: 'hello', timestamp: 1700000000 },
+          { id: 2, role: 'assistant', content: 'hi', timestamp: 1700000001 },
+        ],
+      }
+      getSessionDetailFromDbMock.mockResolvedValue(sessionData)
+
+      const mod = await import('../../packages/server/src/controllers/hermes/sessions')
+      const setMock = vi.fn()
+      const ctx: any = { params: { id: 'txt-123' }, query: { mode: 'full', ext: 'txt' }, set: setMock, body: null }
+
+      await mod.exportSession(ctx)
+
+      expect(setMock).toHaveBeenCalledWith('Content-Type', 'text/plain; charset=utf-8')
+      expect(ctx.body).toContain('# Text Export')
+      expect(ctx.body).toContain('[user]')
+      expect(ctx.body).toContain('hello')
+      expect(ctx.body).toContain('[assistant]')
+      expect(ctx.body).toContain('hi')
+    })
+
+    it('returns 404 when session not found', async () => {
+      getSessionDetailFromDbMock.mockResolvedValue(null)
+      getSessionMock.mockResolvedValue(null)
+
+      const mod = await import('../../packages/server/src/controllers/hermes/sessions')
+      const ctx: any = { params: { id: 'not-found' }, query: {}, set: vi.fn(), body: null }
+
+      await mod.exportSession(ctx)
+
+      expect(ctx.status).toBe(404)
+      expect(ctx.body).toEqual({ error: 'Session not found' })
+    })
+
+    it('falls back to CLI when DB query fails', async () => {
+      const sessionData = { id: 'cli-123', title: 'CLI Session', messages: [] }
+      getSessionDetailFromDbMock.mockRejectedValue(new Error('db unavailable'))
+      getSessionMock.mockResolvedValue(sessionData)
+
+      const mod = await import('../../packages/server/src/controllers/hermes/sessions')
+      const setMock = vi.fn()
+      const ctx: any = { params: { id: 'cli-123' }, query: {}, set: setMock, body: null }
+
+      await mod.exportSession(ctx)
+
+      expect(getSessionMock).toHaveBeenCalledWith('cli-123')
+      expect(JSON.parse(ctx.body)).toMatchObject({ id: 'cli-123' })
+    })
+  })
 })