fix(mobile): keep the live tab's session-option record from eviction

`getScopedRecord` returned an existing record without re-inserting it, so the
per-tab record map evicted by insertion order rather than recency. A long-lived
active tab is the oldest key, so crossing the 32-scope cap silently dropped its
tracked model and reset the pill to "Model". Desktop's scope cache does
delete-then-set for exactly this reason.

Also moves the shared session-option tests to src/shared so the root suite runs
them (they only exercised src/shared logic the Electron renderer consumes, but
sat under mobile/ where only mobile's vitest project sees them), and restores
two "why" comments dropped while extracting the shared modules.

mobile/src/session/use-mobile-native-chat-session-options.test.ts

@@ -135,6 +135,21 @@ describe('useMobileNativeChatSessionOptions', () => {
     expect(effort!.kind).toMatchObject({ currentValue: 'low' })
   })
 
+  it('keeps the live tab’s tracked model when other tabs overflow the record cap', async () => {
+    mount()
+    await act(async () => {
+      await api!.setOption('model', 'opus')
+    })
+    // Far more scopes than the cap, revisiting the live tab in between the way a
+    // chat↔terminal flip does — insertion-order eviction would shed it.
+    for (let index = 0; index < 40; index += 1) {
+      update({ scopeKey: `host\0worktree\0overflow-${index}` })
+      update({ scopeKey: 'host\0worktree\0tab' })
+    }
+    expect(api!.snapshot[0]).toMatchObject({ valueSource: 'dispatched' })
+    expect(api!.snapshot[0]!.kind).toMatchObject({ currentValue: 'opus' })
+  })
+
   it('keeps the latest queued operation pending until it settles', async () => {
     const resolvers: ((outcome: MobileNativeChatSendOutcome) => void)[] = []
     dispatchCommand.mockImplementation(

mobile/src/session/use-mobile-native-chat-session-options.ts

@@ -42,18 +42,21 @@ const recordsByScope = new Map<string, NativeChatSessionOptionRecord>()
 
 function getScopedRecord(scopeKey: string, agent: string): NativeChatSessionOptionRecord {
   const existing = recordsByScope.get(scopeKey)
-  if (existing && existing.agent === agent) {
-    return existing
-  }
-  const created = createNativeChatSessionOptionRecord(agent)
-  if (!recordsByScope.has(scopeKey) && recordsByScope.size >= MOBILE_SESSION_OPTION_RECORD_CAP) {
+  const record =
+    existing && existing.agent === agent ? existing : createNativeChatSessionOptionRecord(agent)
+  // Why: delete-then-set on every read makes the touched scope most-recent, so
+  // eviction only sheds the oldest UNTOUCHED tab. Insertion order alone would let
+  // a long-lived active tab be the oldest key and lose its tracked model.
+  recordsByScope.delete(scopeKey)
+  recordsByScope.set(scopeKey, record)
+  while (recordsByScope.size > MOBILE_SESSION_OPTION_RECORD_CAP) {
     const oldest = recordsByScope.keys().next().value
-    if (oldest !== undefined) {
-      recordsByScope.delete(oldest)
+    if (oldest === undefined) {
+      break
     }
+    recordsByScope.delete(oldest)
   }
-  recordsByScope.set(scopeKey, created)
-  return created
+  return record
 }
 
 export function clearMobileSessionOptionRecordsForTests(): void {

src/shared/native-chat-session-option-commands.test.ts

@@ -2,16 +2,16 @@ import { describe, expect, it } from 'vitest'
 import {
   CLAUDE_SESSION_OPTION_CATALOG,
   CODEX_SESSION_OPTION_CATALOG
-} from '../../../src/shared/agent-session-option-catalog-claude-codex'
+} from './agent-session-option-catalog-claude-codex'
 import {
   buildNativeChatSessionOptionCommand,
   parseBuiltSessionOptionCommand,
   recordNativeChatSessionOptionCommand
-} from '../../../src/shared/native-chat-session-option-commands'
+} from './native-chat-session-option-commands'
 import {
   createNativeChatSessionOptionRecord,
   type NativeChatSessionOptionRecord
-} from '../../../src/shared/native-chat-session-option-state'
+} from './native-chat-session-option-state'
 
 function claudeRecord(model?: string): NativeChatSessionOptionRecord {
   const record = createNativeChatSessionOptionRecord('claude')

src/shared/native-chat-session-option-commands.ts

@@ -109,6 +109,8 @@ function recordCommandApply(args: {
   const previousModelId = typeof record.model?.value === 'string' ? record.model.value : null
   if (optionId === 'model') {
     if (previousModelId !== value) {
+      // Why: a model command can reset model-scoped state, so an older value
+      // from a prior visit is no longer evidence about this live session.
       delete record.valuesByModel[value]
     }
     record.model = { value, source: 'dispatched' }

src/shared/native-chat-session-option-snapshot.test.ts

@@ -2,14 +2,12 @@ import { describe, expect, it } from 'vitest'
 import {
   CLAUDE_SESSION_OPTION_CATALOG,
   CODEX_SESSION_OPTION_CATALOG
-} from '../../../src/shared/agent-session-option-catalog-claude-codex'
+} from './agent-session-option-catalog-claude-codex'
 import {
-  applyNativeChatReportedSessionOptions,
   createNativeChatSessionOptionRecord,
-  matchNativeChatCatalogModelId,
   type NativeChatSessionOptionRecord
-} from '../../../src/shared/native-chat-session-option-state'
-import { buildNativeChatSessionOptionSnapshot } from '../../../src/shared/native-chat-session-option-snapshot'
+} from './native-chat-session-option-state'
+import { buildNativeChatSessionOptionSnapshot } from './native-chat-session-option-snapshot'
 
 function claudeRecord(): NativeChatSessionOptionRecord {
   return createNativeChatSessionOptionRecord('claude')
@@ -96,37 +94,3 @@ describe('buildNativeChatSessionOptionSnapshot', () => {
     expect(fastMode).toMatchObject({ action: { type: 'toggle-command' } })
   })
 })
-
-describe('applyNativeChatReportedSessionOptions', () => {
-  it('reports become authority and reset stale per-model values on a model change', () => {
-    const record = claudeRecord()
-    record.model = { value: 'sonnet', source: 'dispatched' }
-    record.valuesByModel.opus = { effort: { value: 'high', source: 'dispatched' } }
-    expect(applyNativeChatReportedSessionOptions(record, { model: 'opus' })).toBe(true)
-    expect(record.model).toEqual({ value: 'opus', source: 'reported' })
-    // A model change invalidates previously tracked values for the destination.
-    expect(record.valuesByModel.opus).toEqual({})
-  })
-
-  it('is a no-op when the report matches tracked state', () => {
-    const record = claudeRecord()
-    record.model = { value: 'sonnet', source: 'reported' }
-    expect(applyNativeChatReportedSessionOptions(record, { model: 'sonnet' })).toBe(false)
-  })
-})
-
-describe('matchNativeChatCatalogModelId', () => {
-  it('matches exact ids, labels, and provider-id containment', () => {
-    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'sonnet')).toBe('sonnet')
-    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'Sonnet 5')).toBe('sonnet')
-    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'claude-sonnet-5')).toBe(
-      'sonnet'
-    )
-    expect(matchNativeChatCatalogModelId(CODEX_SESSION_OPTION_CATALOG, 'gpt-5.5')).toBe('gpt-5.5')
-  })
-
-  it('returns null for unrecognized reports', () => {
-    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'mystery-model')).toBeNull()
-    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, '')).toBeNull()
-  })
-})

src/shared/native-chat-session-option-snapshot.ts

@@ -58,6 +58,8 @@ function actionForApply(
   if (apply.midSession?.kind === 'agent-picker') {
     return { type: 'agent-picker' }
   }
+  // Why: only unknown flip-only options are actions; once we have a tracked
+  // baseline the UI can show absolute On/Off without inventing a start state.
   return isFlipOnlyMidSession(apply.midSession) && !tracked ? { type: 'toggle-command' } : undefined
 }
 

src/shared/native-chat-session-option-state.test.ts

@@ -0,0 +1,64 @@
+import { describe, expect, it } from 'vitest'
+import {
+  CLAUDE_SESSION_OPTION_CATALOG,
+  CODEX_SESSION_OPTION_CATALOG
+} from './agent-session-option-catalog-claude-codex'
+import {
+  applyNativeChatReportedSessionOptions,
+  createNativeChatSessionOptionRecord,
+  matchNativeChatCatalogModelId,
+  type NativeChatSessionOptionRecord
+} from './native-chat-session-option-state'
+
+function claudeRecord(): NativeChatSessionOptionRecord {
+  return createNativeChatSessionOptionRecord('claude')
+}
+
+describe('applyNativeChatReportedSessionOptions', () => {
+  it('reports become authority and reset stale per-model values on a model change', () => {
+    const record = claudeRecord()
+    record.model = { value: 'sonnet', source: 'dispatched' }
+    record.valuesByModel.opus = { effort: { value: 'high', source: 'dispatched' } }
+    expect(applyNativeChatReportedSessionOptions(record, { model: 'opus' })).toBe(true)
+    expect(record.model).toEqual({ value: 'opus', source: 'reported' })
+    // A model change invalidates previously tracked values for the destination.
+    expect(record.valuesByModel.opus).toEqual({})
+  })
+
+  it('promotes a dispatched guess the report confirms', () => {
+    const record = claudeRecord()
+    record.model = { value: 'sonnet', source: 'dispatched' }
+    expect(applyNativeChatReportedSessionOptions(record, { model: 'sonnet' })).toBe(true)
+    expect(record.model).toEqual({ value: 'sonnet', source: 'reported' })
+  })
+
+  it('keeps locally tracked options when the reported model is unchanged', () => {
+    const record = claudeRecord()
+    record.model = { value: 'sonnet', source: 'reported' }
+    record.valuesByModel.sonnet = { effort: { value: 'high', source: 'dispatched' } }
+    expect(applyNativeChatReportedSessionOptions(record, { model: 'sonnet' })).toBe(false)
+    expect(record.valuesByModel.sonnet?.effort).toEqual({ value: 'high', source: 'dispatched' })
+  })
+
+  it('is a no-op when the report matches tracked state', () => {
+    const record = claudeRecord()
+    record.model = { value: 'sonnet', source: 'reported' }
+    expect(applyNativeChatReportedSessionOptions(record, { model: 'sonnet' })).toBe(false)
+  })
+})
+
+describe('matchNativeChatCatalogModelId', () => {
+  it('matches exact ids, labels, and provider-id containment', () => {
+    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'sonnet')).toBe('sonnet')
+    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'Sonnet 5')).toBe('sonnet')
+    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'claude-sonnet-5')).toBe(
+      'sonnet'
+    )
+    expect(matchNativeChatCatalogModelId(CODEX_SESSION_OPTION_CATALOG, 'gpt-5.5')).toBe('gpt-5.5')
+  })
+
+  it('returns null for unrecognized reports', () => {
+    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, 'mystery-model')).toBeNull()
+    expect(matchNativeChatCatalogModelId(CLAUDE_SESSION_OPTION_CATALOG, '')).toBeNull()
+  })
+})