diff --git a/src/cli/handlers/jira-write.test.ts b/src/cli/handlers/jira-write.test.ts
new file mode 100644
index 00000000000..192fae00a05
--- /dev/null
+++ b/src/cli/handlers/jira-write.test.ts
@@ -0,0 +1,61 @@
+import { describe, expect, it, vi } from 'vitest'
+import { JIRA_AGENT_ACCESS_RUNTIME_CAPABILITY } from '../../shared/jira-agent-capability'
+import { RuntimeClientError } from '../runtime-client'
+import { JIRA_WRITE_HANDLERS } from './jira-write'
+
+function clientFailingWrite(failure: Error) {
+  return vi.fn(async (method: string) => {
+    if (method === 'status.get') {
+      return { result: { capabilities: [JIRA_AGENT_ACCESS_RUNTIME_CAPABILITY] } }
+    }
+    if (method === 'jira.status') {
+      return { result: { sites: [{ id: 'site-1' }], selectedSiteId: 'site-1' } }
+    }
+    throw failure
+  })
+}
+
+async function clearAssigneeAfter(failure: Error): Promise<unknown> {
+  const handler = JIRA_WRITE_HANDLERS['jira assignee clear']
+  try {
+    await handler({
+      // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the handler only calls client.call.
+      client: { call: clientFailingWrite(failure) } as never,
+      cwd: '/tmp',
+      flags: new Map([['key', 'ORCA-1']]),
+      json: false
+    })
+  } catch (error) {
+    return error
+  }
+  throw new Error('expected the write to fail')
+}
+
+// Pins which write failures say "may have been applied" (round-2 S5), so a dropped code is deliberate.
+describe('Jira write outcome-unknown codes', () => {
+  it.each([
+    'runtime_timeout',
+    'runtime_connection_failed',
+    'runtime_disconnected',
+    'runtime_unavailable'
+  ])('reports %s as an unverified write', async (code) => {
+    await expect(
+      clearAssigneeAfter(new RuntimeClientError(code, 'failed.'))
+    ).resolves.toMatchObject({ code: 'jira_write_unverified' })
+  })
+
+  it.each([
+    'remote_runtime_unavailable',
+    'runtime_manually_disconnected',
+    'runtime_source_mismatch',
+    'invalid_argument'
+  ])('passes %s through unchanged', async (code) => {
+    const failure = new RuntimeClientError(code, 'failed.')
+    await expect(clearAssigneeAfter(failure)).resolves.toBe(failure)
+  })
+
+  it('passes a non-client error through unchanged', async () => {
+    const failure = new Error('runtime_timeout')
+    await expect(clearAssigneeAfter(failure)).resolves.toBe(failure)
+  })
+})
diff --git a/src/cli/orchestration-mutation-recovery.test.ts b/src/cli/orchestration-mutation-recovery.test.ts
index 11687285326..92de56f5698 100644
--- a/src/cli/orchestration-mutation-recovery.test.ts
+++ b/src/cli/orchestration-mutation-recovery.test.ts
@@ -314,4 +314,19 @@ describe('orchestration mutation recovery', () => {
     expect(result.data).not.toHaveProperty('originalCommand')
     expect((result.data as { recovery: object }).recovery).not.toHaveProperty('retryCommand')
   })
+
+  // Pins the outcome-unknown codes (round-2 S5): only these get recovery guidance.
+  it.each([
+    ['runtime_unavailable', true],
+    ['remote_runtime_unavailable', true],
+    ['runtime_timeout', true],
+    ['invalid_runtime_response', true],
+    ['runtime_manually_disconnected', false],
+    ['remote_runtime_timeout', false],
+    ['runtime_rpc_queue_overloaded', false],
+    ['invalid_argument', false]
+  ])('treats %s as an unknown mutation outcome: %s', (code, unknown) => {
+    const error = new RuntimeClientError(code, 'failed', { orchestrationRequestId: 'request-1' })
+    expect(orchestrationMutationRecoveryError(error) !== error).toBe(unknown)
+  })
 })
diff --git a/src/renderer/src/components/automations/automation-host-cache-error.test.ts b/src/renderer/src/components/automations/automation-host-cache-error.test.ts
new file mode 100644
index 00000000000..00ab40d36a4
--- /dev/null
+++ b/src/renderer/src/components/automations/automation-host-cache-error.test.ts
@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest'
+import { RemoteRuntimeClientError } from '../../../../shared/remote-runtime-client-error'
+import { classifyAutomationHostQueryError } from './automation-host-cache-error'
+
+function classify(error: unknown): { code: string; retryable: boolean } {
+  const { code, retryable } = classifyAutomationHostQueryError(error, { attempt: 1, now: 0 })
+  return { code, retryable }
+}
+
+// Pins the RPC-code mapping of host query failures (round-2 S5), so a dropped code is deliberate.
+describe('classifyAutomationHostQueryError code mapping', () => {
+  it.each([
+    ['runtime_unavailable', 'authority_unavailable', true],
+    ['remote_runtime_unavailable', 'authority_unavailable', true],
+    ['relay_quota_exceeded', 'authority_unavailable', true],
+    ['timeout', 'timeout', true],
+    ['runtime_timeout', 'timeout', true],
+    ['permission_denied', 'permission_denied', false],
+    ['unauthorized', 'permission_denied', false],
+    ['forbidden', 'permission_denied', false],
+    ['capability_unsupported', 'incompatible', false],
+    ['legacy_read_only', 'incompatible', false],
+    ['invalid_runtime_response', 'invalid_response', false],
+    ['invalid_argument', 'invalid_response', false],
+    ['runtime_manually_disconnected', 'unknown', true],
+    ['runtime_rpc_queue_overloaded', 'unknown', true],
+    ['remote_runtime_busy', 'unknown', true]
+  ])('maps %s to %s (retryable: %s)', (rpcCode, code, retryable) => {
+    expect(classify(new RemoteRuntimeClientError(rpcCode, 'failed'))).toEqual({ code, retryable })
+  })
+
+  it('reads a code-stripped message token', () => {
+    expect(
+      classify(new Error("Error invoking remote method 'x': Error: failed: runtime_timeout"))
+    ).toEqual({ code: 'timeout', retryable: true })
+  })
+})
diff --git a/src/renderer/src/lib/launch-structured-agent-session.test.ts b/src/renderer/src/lib/launch-structured-agent-session.test.ts
index 91f8b9839c6..d0244000790 100644
--- a/src/renderer/src/lib/launch-structured-agent-session.test.ts
+++ b/src/renderer/src/lib/launch-structured-agent-session.test.ts
@@ -524,4 +524,37 @@ describe('structured agent session launch', () => {
 
     expect(transportError).not.toBeInstanceOf(StructuredAgentSessionCreateRefusalError)
   })
+
+  // Pins the thrown-error half (round-2 S5): a host that flattened the refusal to runtime_error
+  // still ends it with the token, and client-minted codes never prove nothing was created.
+  it('reads a definitive token from a flattened runtime_error message', async () => {
+    mockSupportedCreate(() => {
+      throw Object.assign(new Error('structured_agent_session_unsupported'), {
+        code: 'runtime_error'
+      })
+    })
+    const error = await launchStructuredAgentSession(
+      createStructuredAgentSessionLaunchIntent('workspace-flattened-refusal', 'codex')
+    ).catch((caught: unknown) => caught)
+
+    expect(error).toBeInstanceOf(StructuredAgentSessionCreateRefusalError)
+    expect(error).toMatchObject({ code: 'structured_agent_session_unsupported' })
+  })
+
+  it.each([
+    'runtime_manually_disconnected',
+    'runtime_rpc_queue_overloaded',
+    'runtime_unavailable',
+    'remote_runtime_unavailable',
+    'method_not_supported'
+  ])('keeps a thrown %s outcome unknown', async (code) => {
+    mockSupportedCreate(() => {
+      throw Object.assign(new Error('failed'), { code })
+    })
+    const error = await launchStructuredAgentSession(
+      createStructuredAgentSessionLaunchIntent(`workspace-client-${code}`, 'codex')
+    ).catch((caught: unknown) => caught)
+
+    expect(error).not.toBeInstanceOf(StructuredAgentSessionCreateRefusalError)
+  })
 })
diff --git a/src/renderer/src/runtime/web-runtime-browser-creation-failure.test.ts b/src/renderer/src/runtime/web-runtime-browser-creation-failure.test.ts
new file mode 100644
index 00000000000..df992bad397
--- /dev/null
+++ b/src/renderer/src/runtime/web-runtime-browser-creation-failure.test.ts
@@ -0,0 +1,79 @@
+import { describe, expect, it, vi } from 'vitest'
+import { RemoteRuntimeClientError } from '../../../shared/remote-runtime-client-error'
+import type { WebRuntimeBrowserCreationContext } from './web-runtime-browser-creation-context'
+import { prepareWebRuntimeBrowserCreationFailure } from './web-runtime-browser-creation-failure'
+
+vi.mock('../store', () => ({ useAppStore: { getState: vi.fn(), setState: vi.fn() } }))
+
+function failedCreateContext(): WebRuntimeBrowserCreationContext {
+  return {
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the failure path reads only worktreeId and the group fields, which are absent here.
+    args: { worktreeId: 'repo::/w' } as never,
+    environmentId: 'env-1',
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the prepare step never reads the intent owner.
+    intentOwner: {} as never,
+    // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the prepare step never calls the environment.
+    callEnvironment: vi.fn() as never,
+    shouldFocusOnCreate: false,
+    shouldSelectWorktree: false,
+    provisionalPageId: 'provisional-page',
+    hostSupportsKnownPageId: true,
+    expectsClientHosting: false,
+    unsubscribeFocusGuard: vi.fn(),
+    guardedPageId: 'provisional-page',
+    createdPageId: null,
+    createAttempted: true,
+    staged: null
+  }
+}
+
+function prepare(error: unknown): { cleanupPageId: string | null; createOutcomeUnknown: boolean } {
+  const { cleanupPageId, createOutcomeUnknown } = prepareWebRuntimeBrowserCreationFailure(
+    failedCreateContext(),
+    error
+  )
+  return { cleanupPageId, createOutcomeUnknown }
+}
+
+// Pins which create failures prove no page exists (round-2 S5), so a dropped code is deliberate.
+describe('prepareWebRuntimeBrowserCreationFailure definitive codes', () => {
+  it.each([
+    'browser_error',
+    'capability_unsupported',
+    'invalid_argument',
+    'invalid_params',
+    'method_not_found',
+    'runtime_rpc_queue_overloaded',
+    'selector_ambiguous',
+    'selector_not_found',
+    'unauthorized'
+  ])('skips the provisional-page cleanup after %s', (code) => {
+    expect(prepare(new RemoteRuntimeClientError(code, 'failed'))).toEqual({
+      cleanupPageId: null,
+      createOutcomeUnknown: false
+    })
+  })
+
+  it.each([
+    'runtime_manually_disconnected',
+    'runtime_unavailable',
+    'remote_runtime_unavailable',
+    'runtime_timeout',
+    'remote_runtime_busy',
+    'runtime_error'
+  ])('cleans up the provisional page after %s', (code) => {
+    expect(prepare(new RemoteRuntimeClientError(code, 'failed'))).toEqual({
+      cleanupPageId: 'provisional-page',
+      createOutcomeUnknown: false
+    })
+  })
+
+  it('reads a definitive code from a code-stripped message token', () => {
+    expect(
+      prepare(new Error("Error invoking remote method 'x': Error: failed: method_not_found"))
+    ).toEqual({
+      cleanupPageId: null,
+      createOutcomeUnknown: false
+    })
+  })
+})
diff --git a/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts b/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts
new file mode 100644
index 00000000000..b6ba507f063
--- /dev/null
+++ b/src/renderer/src/runtime/web-runtime-session-tab-close-undelivered-codes.test.ts
@@ -0,0 +1,185 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import type * as TrackingDecisions from './web-session-tabs-sync/tracking-decisions'
+import { closeWebRuntimeSessionTab } from './web-runtime-session-tab-lifecycle'
+import {
+  resetWebSessionCloseReplaysForTests,
+  takeDueWebSessionCloseReplays
+} from './web-session-close-replay'
+import { resetWebSessionFocusIntentForTests } from './web-session-focus-intent'
+import {
+  isWebSessionCloseIntentPending,
+  resetWebSessionCloseIntentForTests
+} from './web-session-close-intent'
+import { ENVIRONMENT_ID, WORKTREE_ID } from './web-runtime-session-test-harness'
+import { stubRuntimeEnvironmentBridge } from './runtime-environment-bridge-fixture'
+
+const mocks = vi.hoisted(() => ({
+  getState: vi.fn(),
+  setState: vi.fn(),
+  subscribe: vi.fn(),
+  setActiveWorktree: vi.fn(),
+  createBrowserTab: vi.fn(),
+  closeEmptyGroup: vi.fn(),
+  moveUnifiedTabToGroup: vi.fn(),
+  setRemoteBrowserPageHandle: vi.fn(),
+  focusBrowserTabInWorktree: vi.fn(),
+  applyWebSessionTabsSnapshot: vi.fn(),
+  decideWebSessionTabsSnapshot: vi.fn(() => ({ apply: true, settlesHostMirror: true })),
+  getWebSessionTabsTrackingGeneration: vi.fn(() => 0),
+  acceptReplayedWebSessionTabsSnapshot: vi.fn(),
+  resolveHostSessionTabIdForWebSessionTab: vi.fn(),
+  trackTerminalPaneSplit: vi.fn(),
+  deliverLaunchPromptToAgentTab: vi.fn(),
+  seedNativeChatLaunchDraftForAgentTab: vi.fn(),
+  getRuntimeEnvironmentIdForWorktree: vi.fn(),
+  hasMaterializedWebRuntimeBrowserPage: vi.fn()
+}))
+
+vi.mock('../store', () => ({
+  useAppStore: {
+    getState: mocks.getState,
+    setState: mocks.setState,
+    subscribe: mocks.subscribe
+  }
+}))
+
+vi.mock('./web-session-tabs-sync/tracking-lifecycle', () => ({
+  acceptReplayedWebSessionTabsSnapshot: mocks.acceptReplayedWebSessionTabsSnapshot,
+  getWebSessionTabsTrackingGeneration: mocks.getWebSessionTabsTrackingGeneration
+}))
+vi.mock('./web-session-tabs-sync/snapshot-api', () => ({
+  applyWebSessionTabsSnapshot: mocks.applyWebSessionTabsSnapshot
+}))
+vi.mock('./web-session-tabs-sync/tracking-decisions', async (importOriginal) => ({
+  ...(await importOriginal<typeof TrackingDecisions>()),
+  decideWebSessionTabsSnapshot: mocks.decideWebSessionTabsSnapshot
+}))
+vi.mock('./web-session-tabs-sync/store-patch', () => ({
+  applyWebSessionTabsStorePatch: (buildPatch: (state: unknown) => unknown) => {
+    mocks.setState(buildPatch)
+    // The production caller invokes the returned settle receipt.
+    return () => {}
+  }
+}))
+vi.mock('./web-session-tabs-sync/tracking-mappings', () => ({
+  resolveHostSessionTabIdForWebSessionTab: mocks.resolveHostSessionTabIdForWebSessionTab
+}))
+
+vi.mock('@/lib/feature-education-telemetry', () => ({
+  trackTerminalPaneSplit: mocks.trackTerminalPaneSplit
+}))
+
+vi.mock('@/lib/worktree-runtime-owner', () => ({
+  getRuntimeEnvironmentIdForWorktree: mocks.getRuntimeEnvironmentIdForWorktree
+}))
+
+vi.mock('@/lib/agent-launch-prompt-delivery', () => ({
+  deliverLaunchPromptToAgentTab: mocks.deliverLaunchPromptToAgentTab,
+  seedNativeChatLaunchDraftForAgentTab: mocks.seedNativeChatLaunchDraftForAgentTab
+}))
+
+vi.mock('./web-runtime-browser-materialization', () => ({
+  hasMaterializedWebRuntimeBrowserPage: mocks.hasMaterializedWebRuntimeBrowserPage
+}))
+
+afterEach(() => {
+  resetWebSessionCloseIntentForTests()
+  resetWebSessionCloseReplaysForTests()
+})
+
+const OWNER = { environmentId: ENVIRONMENT_ID }
+
+async function closeAfter(failure: unknown, rejects = false): Promise<boolean> {
+  const runtimeCall = vi.fn()
+  if (rejects) {
+    runtimeCall.mockRejectedValueOnce(failure)
+  } else {
+    runtimeCall.mockResolvedValueOnce(failure)
+  }
+  runtimeCall.mockResolvedValue({ id: 'close', ok: true, result: { closed: true } })
+  stubRuntimeEnvironmentBridge({ call: runtimeCall })
+  await expect(
+    closeWebRuntimeSessionTab({
+      worktreeId: WORKTREE_ID,
+      tabId: 'local-browser-unified',
+      reason: 'user'
+    })
+  ).resolves.toBe('failed')
+  const held = isWebSessionCloseIntentPending(
+    OWNER,
+    WORKTREE_ID,
+    'host-browser-unified',
+    Date.now() + 60_000
+  )
+  const replayQueued =
+    takeDueWebSessionCloseReplays(OWNER, WORKTREE_ID, new Set(['host-browser-unified'])).length > 0
+  expect(replayQueued).toBe(held)
+  return held
+}
+
+function envelope(code: string): unknown {
+  return { id: 'close', ok: false, error: { code, message: 'failed' } }
+}
+
+// Pins which close failures keep the user's close for replay (round-2 S5), so a dropped code is deliberate.
+describe('user close: which failures keep the intent', () => {
+  beforeEach(() => {
+    vi.stubGlobal('__ORCA_WEB_CLIENT__', true)
+    mocks.getState.mockReturnValue({
+      settings: {
+        activeRuntimeEnvironmentId: ENVIRONMENT_ID
+      },
+      tabsByWorktree: {},
+      terminalLayoutsByTabId: {},
+      activeTabIdByWorktree: {},
+      activeGroupIdByWorktree: {},
+      setActiveWorktree: mocks.setActiveWorktree
+    })
+    mocks.resolveHostSessionTabIdForWebSessionTab.mockImplementation(
+      (_state, args: { tabId: string }) =>
+        args.tabId === 'local-browser-unified' ? 'host-browser-unified' : null
+    )
+    // Store patches must run their updater so snapshot reconciliation is observable.
+    mocks.setState.mockImplementation((updater: (state: unknown) => unknown) => {
+      updater({
+        state: 'before',
+        activeWorktreeId: WORKTREE_ID
+      })
+    })
+    mocks.applyWebSessionTabsSnapshot.mockReturnValue({ state: 'after' })
+  })
+
+  afterEach(() => {
+    resetWebSessionFocusIntentForTests()
+    vi.unstubAllGlobals()
+    vi.clearAllMocks()
+  })
+
+  it.each([
+    'runtime_manually_disconnected',
+    'runtime_unavailable',
+    'remote_runtime_unavailable',
+    'runtime_timeout',
+    'remote_runtime_timeout'
+  ])('keeps the close when the answer is %s', async (code) => {
+    expect(await closeAfter(envelope(code))).toBe(true)
+  })
+
+  // #30146: the web client mints this as a bare Error; it must never drop the close.
+  it('keeps the close when the client itself refuses with runtime_manually_disconnected', async () => {
+    expect(await closeAfter(new Error('runtime_manually_disconnected'), true)).toBe(true)
+  })
+
+  it('keeps the close on any thrown transport failure', async () => {
+    expect(await closeAfter(new Error('socket hang up'), true)).toBe(true)
+  })
+
+  it.each([
+    'invalid_argument',
+    'runtime_rpc_queue_overloaded',
+    'ssh_user_disconnected',
+    'conflict'
+  ])('drops the close when the answer is %s', async (code) => {
+    expect(await closeAfter(envelope(code))).toBe(false)
+  })
+})
diff --git a/src/renderer/src/runtime/web-session-terminal-orphan-recovery-adoption.test.ts b/src/renderer/src/runtime/web-session-terminal-orphan-recovery-adoption.test.ts
new file mode 100644
index 00000000000..a285c53800c
--- /dev/null
+++ b/src/renderer/src/runtime/web-session-terminal-orphan-recovery-adoption.test.ts
@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'vitest'
+import { isStableAdoptionFailure } from './web-session-terminal-orphan-recovery-adoption'
+
+function failure(code: string, message = 'refused'): unknown {
+  return { id: 'adopt', ok: false, error: { code, message } }
+}
+
+// Pins which adoption failures stop retrying (round-2 S5), so a dropped code is deliberate.
+describe('isStableAdoptionFailure', () => {
+  it.each(['method_not_found', 'capability_unsupported', 'invalid_runtime_response'])(
+    'treats %s as stable',
+    (code) => {
+      expect(isStableAdoptionFailure(failure(code))).toBe(true)
+    }
+  )
+
+  it.each([
+    'remote_runtime_unavailable',
+    'remote_runtime_busy',
+    'runtime_rpc_queue_overloaded',
+    'runtime_timeout',
+    'runtime_unavailable',
+    'reconnecting',
+    'timeout',
+    'runtime_manually_disconnected',
+    'terminal_not_found'
+  ])('keeps retrying after %s', (code) => {
+    expect(isStableAdoptionFailure(failure(code))).toBe(false)
+  })
+
+  it('keeps retrying a code-stripped connection failure even if it names a stable code', () => {
+    expect(
+      isStableAdoptionFailure(
+        new Error('Could not connect to the remote Orca runtime: method_not_found')
+      )
+    ).toBe(false)
+  })
+
+  it('reads a stable code from a thrown error message token', () => {
+    expect(isStableAdoptionFailure(new Error('Adoption failed: capability_unsupported'))).toBe(true)
+  })
+})
diff --git a/src/renderer/src/startup/startup-web-host-unreachable.test.ts b/src/renderer/src/startup/startup-web-host-unreachable.test.ts
new file mode 100644
index 00000000000..0b7377b4de6
--- /dev/null
+++ b/src/renderer/src/startup/startup-web-host-unreachable.test.ts
@@ -0,0 +1,68 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { RemoteRuntimeClientError } from '../../../shared/remote-runtime-client-error'
+import { isWebHostUnreachableAtStartup } from './startup-web-host-unreachable'
+
+vi.mock('sonner', () => ({ toast: vi.fn() }))
+
+function stubWindow(webClient: boolean, snapshots: unknown[]): void {
+  vi.stubGlobal('window', {
+    __ORCA_WEB_CLIENT__: webClient,
+    api: { runtimeEnvironments: { getStatusSnapshots: vi.fn(async () => snapshots) } }
+  })
+}
+
+// Pins which boot failures read as "host unreachable" (round-2 S5), so a dropped code is deliberate.
+describe('isWebHostUnreachableAtStartup', () => {
+  beforeEach(() => {
+    stubWindow(true, [])
+  })
+
+  afterEach(() => {
+    vi.unstubAllGlobals()
+  })
+
+  it.each([
+    'remote_runtime_unavailable',
+    'remote_runtime_busy',
+    'runtime_rpc_queue_overloaded',
+    'runtime_timeout',
+    'runtime_unavailable',
+    'reconnecting',
+    'timeout'
+  ])('treats %s as unreachable while the transport is down', async (code) => {
+    await expect(
+      isWebHostUnreachableAtStartup(new RemoteRuntimeClientError(code, 'failed'))
+    ).resolves.toBe(true)
+  })
+
+  it.each([
+    'Timed out while connecting to the remote Orca runtime.',
+    'Remote Orca runtime connection interrupted.',
+    'Could not connect to the remote Orca runtime.'
+  ])('treats the code-less message "%s" as unreachable', async (message) => {
+    await expect(isWebHostUnreachableAtStartup(new Error(message))).resolves.toBe(true)
+  })
+
+  it.each(['runtime_manually_disconnected', 'invalid_runtime_response', 'unauthorized'])(
+    'treats %s as a hydration fault',
+    async (code) => {
+      await expect(
+        isWebHostUnreachableAtStartup(new RemoteRuntimeClientError(code, 'failed'))
+      ).resolves.toBe(false)
+    }
+  )
+
+  it('treats a connection failure on a ready transport as a hydration fault', async () => {
+    stubWindow(true, [{ transport: 'ready', retired: false }])
+    await expect(
+      isWebHostUnreachableAtStartup(new RemoteRuntimeClientError('runtime_timeout', 'failed'))
+    ).resolves.toBe(false)
+  })
+
+  it('is never true outside the web client', async () => {
+    stubWindow(false, [])
+    await expect(
+      isWebHostUnreachableAtStartup(new RemoteRuntimeClientError('runtime_timeout', 'failed'))
+    ).resolves.toBe(false)
+  })
+})
diff --git a/src/renderer/src/store/slices/worktrees/teardown/host-worktree-removal-state.test.ts b/src/renderer/src/store/slices/worktrees/teardown/host-worktree-removal-state.test.ts
new file mode 100644
index 00000000000..d5d17019aef
--- /dev/null
+++ b/src/renderer/src/store/slices/worktrees/teardown/host-worktree-removal-state.test.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it } from 'vitest'
+import { RemoteRuntimeClientError } from '../../../../../../shared/remote-runtime-client-error'
+import { RuntimeRpcCallQueueOverloadError } from '../../../../../../shared/runtime-rpc-call-queue'
+import { isWorktreeRemovalReplyLost } from './host-worktree-removal-state'
+
+// Pins which delete failures wait on the host's listing (round-2 S5), so a dropped code is deliberate.
+describe('isWorktreeRemovalReplyLost', () => {
+  it.each([
+    'remote_runtime_unavailable',
+    'remote_runtime_busy',
+    'runtime_timeout',
+    'runtime_unavailable',
+    'reconnecting',
+    'timeout'
+  ])('treats %s as a lost reply', (code) => {
+    expect(isWorktreeRemovalReplyLost(new RemoteRuntimeClientError(code, 'transport failed'))).toBe(
+      true
+    )
+  })
+
+  it('treats a queue overload as never sent', () => {
+    expect(isWorktreeRemovalReplyLost(new RuntimeRpcCallQueueOverloadError('global'))).toBe(false)
+    expect(
+      isWorktreeRemovalReplyLost(
+        new Error(
+          "Error invoking remote method 'x': Error: Remote runtime call queue is full; retry after current calls finish."
+        )
+      )
+    ).toBe(false)
+  })
+
+  it.each([
+    'runtime_manually_disconnected',
+    'invalid_runtime_response',
+    'unauthorized',
+    'worktree_not_found'
+  ])('does not treat %s as a lost reply', (code) => {
+    expect(isWorktreeRemovalReplyLost(new RemoteRuntimeClientError(code, 'refused'))).toBe(false)
+  })
+
+  it.each([
+    "Error invoking remote method 'x': Error: Request timed out.",
+    "Error invoking remote method 'x': Error: Remote Orca runtime connection interrupted.",
+    "Error invoking remote method 'x': Error: Could not connect to the remote Orca runtime."
+  ])('treats the code-stripped message "%s" as a lost reply', (message) => {
+    expect(isWorktreeRemovalReplyLost(new Error(message))).toBe(true)
+  })
+})
diff --git a/src/shared/agent-session-definitive-refusal.test.ts b/src/shared/agent-session-definitive-refusal.test.ts
index ac4aca0964f..ed3141dbb02 100644
--- a/src/shared/agent-session-definitive-refusal.test.ts
+++ b/src/shared/agent-session-definitive-refusal.test.ts
@@ -38,4 +38,19 @@ describe('definitive agent-session create refusals', () => {
     )
     expect(isDefinitiveAgentSessionCreateRefusal('structured_agent_session_unsupported')).toBe(true)
   })
+
+  // Pins the RPC half (round-2 S5): transport and client-minted codes never allow a fallback.
+  it.each([
+    'runtime_unavailable',
+    'remote_runtime_unavailable',
+    'runtime_timeout',
+    'runtime_manually_disconnected',
+    'runtime_rpc_queue_overloaded',
+    'method_not_supported',
+    'invalid_argument',
+    null,
+    undefined
+  ])('does not count %s as definitive', (code) => {
+    expect(isDefinitiveAgentSessionCreateRefusal(code)).toBe(false)
+  })
 })
diff --git a/src/shared/remote-runtime-client-error-classification.test.ts b/src/shared/remote-runtime-client-error-classification.test.ts
index ef33c0c376e..c7141e60df9 100644
--- a/src/shared/remote-runtime-client-error-classification.test.ts
+++ b/src/shared/remote-runtime-client-error-classification.test.ts
@@ -1,5 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import {
+  RECOVERABLE_CODES,
+  RECOVERABLE_MESSAGE_FRAGMENTS,
   isRecoverableRemoteRuntimeConnectionError,
   isRuntimeRpcQueueOverloadError,
   toRemoteRuntimeClientErrorLike
@@ -61,4 +63,54 @@ describe('remote runtime client error classification', () => {
     const error = toRemoteRuntimeClientErrorLike(new Error(message))
     expect(isRecoverableRemoteRuntimeConnectionError(error)).toBe(true)
   })
+
+  // Pins the list so a dropped or added code is a deliberate, reviewed change (round-2 S5).
+  it('pins the recoverable codes and message fragments', () => {
+    expect([...RECOVERABLE_CODES].toSorted()).toEqual([
+      'reconnecting',
+      'remote_runtime_busy',
+      'remote_runtime_unavailable',
+      'runtime_rpc_queue_overloaded',
+      'runtime_timeout',
+      'runtime_unavailable',
+      'timeout'
+    ])
+    expect(RECOVERABLE_MESSAGE_FRAGMENTS).toEqual([
+      'could not connect to the remote orca runtime',
+      'remote orca runtime closed the connection',
+      'remote orca runtime connection closed',
+      'remote orca runtime is not connected',
+      'remote runtime call queue is full',
+      'remote runtime connection closed',
+      'remote runtime connection wait limit reached',
+      'remote runtime request limit reached',
+      'remote runtime subscription limit reached',
+      'remote runtime subscription memory limit reached',
+      'remote runtime subscription closed before it started',
+      'remote terminal stream is not connected',
+      'timed out waiting for the remote orca runtime'
+    ])
+  })
+
+  it.each([
+    'runtime_manually_disconnected',
+    'ssh_user_disconnected',
+    'remote_runtime_timeout',
+    'runtime_busy'
+  ])('does not treat client code %s as recoverable', (code) => {
+    expect(isRecoverableRemoteRuntimeConnectionError({ code, message: 'refused' })).toBe(false)
+  })
+
+  it.each(RECOVERABLE_MESSAGE_FRAGMENTS)(
+    'recovers a code-stripped message containing %s',
+    (fragment) => {
+      expect(
+        isRecoverableRemoteRuntimeConnectionError(
+          toRemoteRuntimeClientErrorLike(
+            new Error(`Error invoking remote method 'x': Error: ${fragment}.`)
+          )
+        )
+      ).toBe(true)
+    }
+  )
 })
diff --git a/src/shared/structured-agent-session-send-evidence.test.ts b/src/shared/structured-agent-session-send-evidence.test.ts
index db8a8a7ee68..c4dadb66c77 100644
--- a/src/shared/structured-agent-session-send-evidence.test.ts
+++ b/src/shared/structured-agent-session-send-evidence.test.ts
@@ -98,6 +98,15 @@ describe('structuredAgentSessionSendEvidence', () => {
     ]) {
       expect(structuredAgentSessionSendEvidence(thrown(rpcCode)).kind).toBe('uncertain')
     }
+    for (const rpcCode of [
+      'runtime_manually_disconnected',
+      'runtime_rpc_queue_overloaded',
+      'remote_runtime_busy',
+      'forbidden',
+      'capability_unsupported'
+    ]) {
+      expect(structuredAgentSessionSendEvidence(thrown(rpcCode)).kind).toBe('uncertain')
+    }
     const thrownRefusal = {
       response: { error: { data: { refusal: { code: 'agent_session_journal_unreadable' } } } }
     }
@@ -110,8 +119,14 @@ describe('structuredAgentSessionSendEvidence', () => {
     ).toBe('uncertain')
   })
 
+  // Pins the full turned-away list (round-2 S5): every other code, client-minted ones included, is uncertain.
   it('treats a call the host turned away before running it as never written', () => {
-    for (const rpcCode of ['method_not_found', 'invalid_argument', 'unauthorized']) {
+    for (const rpcCode of [
+      'method_not_found',
+      'method_not_supported',
+      'invalid_argument',
+      'unauthorized'
+    ]) {
       expect(structuredAgentSessionSendEvidence(thrown(rpcCode)).kind).toBe('not-recorded')
     }
   })