diff --git a/src/cli/format.ts b/src/cli/format.ts
index 8707ceef092..f72aafdf660 100644
--- a/src/cli/format.ts
+++ b/src/cli/format.ts
@@ -246,7 +246,15 @@ export function formatCliStatus(status: CliStatusResult): string {
     `runtimeState: ${status.runtime.state}`,
     `runtimeReachable: ${status.runtime.reachable}`,
     `runtimeId: ${status.runtime.runtimeId ?? 'none'}`,
-    `graphState: ${status.graph.state}`
+    `graphState: ${status.graph.state}`,
+    // Why: STA-3969 — an unreachable runtime is only actionable if the plain-text
+    // output carries the cause, not just the state word.
+    ...(status.runtime.unreachableReason
+      ? [
+          `unreachableCode: ${status.runtime.unreachableReason.code}`,
+          `unreachableDetail: ${status.runtime.unreachableReason.message}`
+        ]
+      : [])
   ].join('\n')
 }
 
diff --git a/src/cli/runtime-client.test.ts b/src/cli/runtime-client.test.ts
index 2fa6130ce3d..73aad83b6a7 100644
--- a/src/cli/runtime-client.test.ts
+++ b/src/cli/runtime-client.test.ts
@@ -1,4 +1,4 @@
-import { mkdtempSync, writeFileSync } from 'node:fs'
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import { createServer, type Socket } from 'node:net'
@@ -316,6 +316,163 @@ describe.skipIf(process.platform === 'win32')('RuntimeClient', () => {
     expect(launchOrcaApp).toHaveBeenCalledOnce()
   })
 
+  // STA-3969: this loop only polls getCliStatus, so an unreachable runtime used to
+  // burn the whole budget and then report a bare timeout — the third symptom in the
+  // report, and the one that reads as "the app never finished starting".
+  it('openOrca reports why the runtime was unreachable instead of a bare timeout', async () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
+    writeMetadata(userDataPath, join(userDataPath, 'never-listened.sock'), 'token', process.pid)
+
+    const client = new RuntimeClient(userDataPath, 100)
+
+    await expect(client.openOrca(100)).rejects.toMatchObject({
+      code: 'runtime_open_timeout',
+      message: expect.stringContaining('never-listened.sock'),
+      data: { unreachableReason: { code: 'endpoint_missing' } }
+    })
+  })
+
+  // STA-3969: the diagnosis is still worth surfacing once metadata disappears, but the newest
+  // poll no longer observes it -- so it is reported as the last failure seen, not as the live
+  // one. Presenting it under `unreachableReason` would be the same stale negative in machine form.
+  it('reports the last unreachable reason as history when later polls have no metadata', async () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
+    writeMetadata(userDataPath, join(userDataPath, 'never-listened.sock'), 'token', process.pid)
+    vi.mocked(launchOrcaApp).mockImplementationOnce(() => {
+      rmSync(join(userDataPath, 'orca-runtime.json'))
+    })
+
+    const client = new RuntimeClient(userDataPath, 100)
+
+    const failure = await client.openOrca(100).then(
+      () => null,
+      (error: unknown) => error as { code: string; message: string; data?: unknown }
+    )
+    expect(failure?.code).toBe('runtime_open_timeout')
+    expect(failure?.message).toContain('never-listened.sock')
+    expect(failure?.message).toContain('The last failure it reported was')
+    expect(failure?.message).not.toContain('the Orca app process is running')
+    const data = failure?.data as {
+      unreachableReason?: unknown
+      lastObservedUnreachableReason?: { code?: string }
+    }
+    expect(data.unreachableReason).toBeUndefined()
+    expect(data.lastObservedUnreachableReason?.code).toBe('endpoint_missing')
+  })
+
+  // STA-3969: same stale negative one state further along -- the runtime was unreachable, then
+  // its PROCESS exited. The newest poll reports a dead process and no reason, so quoting the old
+  // endpoint failure claims a running process the latest status denies.
+  it('openOrca stops claiming the process is running once it exits mid-wait', async () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
+    const endpoint = join(userDataPath, 'never-listened.sock')
+    writeMetadata(userDataPath, endpoint, 'token', process.pid)
+    vi.mocked(launchOrcaApp).mockImplementationOnce(() => {
+      writeMetadata(userDataPath, endpoint, 'token', findUnusedPid())
+    })
+
+    const client = new RuntimeClient(userDataPath, 100)
+
+    const failure = await client.openOrca(100).then(
+      () => null,
+      (error: unknown) => error as { code: string; message: string; data?: unknown }
+    )
+    expect(failure?.code).toBe('runtime_open_timeout')
+    expect(failure?.message).not.toContain('the Orca app process is running')
+    expect(failure?.message).toContain('no longer running')
+    expect(
+      (failure?.data as { unreachableReason?: unknown } | undefined)?.unreachableReason
+    ).toBeUndefined()
+  })
+
+  // STA-3969: `request_rejected` means the runtime ANSWERED and refused. Calling that
+  // "unreachable" contradicts the very reason being quoted alongside it.
+  it('openOrca says the runtime refused the request instead of calling it unreachable', async () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
+    const endpoint = join(userDataPath, 'runtime.sock')
+    const server = createServer((socket) => {
+      sockets.add(socket)
+      socket.once('close', () => sockets.delete(socket))
+      socket.on('data', (data) => {
+        const request = JSON.parse(String(data).trim()) as { id: string }
+        socket.write(
+          `${JSON.stringify({
+            id: request.id,
+            ok: false,
+            error: { code: 'status_refused', message: 'status.get is disabled' }
+          })}\n`
+        )
+      })
+    })
+    servers.add(server)
+    await new Promise<void>((resolve) => server.listen(endpoint, resolve))
+    writeMetadata(userDataPath, endpoint, 'token', process.pid)
+
+    const client = new RuntimeClient(userDataPath, 100)
+
+    const failure = await client.openOrca(100).then(
+      () => null,
+      (error: unknown) => error as { code: string; message: string; data?: unknown }
+    )
+    expect(failure?.code).toBe('runtime_open_timeout')
+    expect(
+      (failure?.data as { unreachableReason?: { code?: string } } | undefined)?.unreachableReason
+        ?.code
+    ).toBe('request_rejected')
+    expect(failure?.message).toContain('refused the status request')
+    expect(failure?.message).not.toContain('its runtime is unreachable')
+  })
+
+  // STA-3969: the poll carried the earlier reason forward with `?? lastReason`, so a runtime
+  // that RECOVERED mid-wait was still reported unreachable at the timeout -- a stale negative
+  // presented as the current diagnosis.
+  it('openOrca stops reporting a runtime unreachable once it answers again', async () => {
+    const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
+    const endpoint = join(userDataPath, 'runtime.sock')
+    const server = createServer((socket) => {
+      sockets.add(socket)
+      socket.once('close', () => sockets.delete(socket))
+      socket.once('data', (data) => {
+        const request = JSON.parse(String(data).trim()) as { id: string }
+        socket.write(
+          `${JSON.stringify({
+            id: request.id,
+            ok: true,
+            result: {
+              runtimeId: 'runtime-1',
+              rendererGraphEpoch: 0,
+              graphStatus: 'ready',
+              authoritativeWindowId: 0,
+              desktopWindowStatus: 'initializing',
+              liveTabCount: 0,
+              liveLeafCount: 0
+            },
+            _meta: { runtimeId: 'runtime-1' }
+          })}\n`
+        )
+      })
+    })
+    servers.add(server)
+    await new Promise<void>((resolve) => server.listen(endpoint, resolve))
+    // Starts pointed at an endpoint nothing serves, then recovers onto the live one.
+    writeMetadata(userDataPath, join(userDataPath, 'never-listened.sock'), 'token', process.pid)
+    vi.mocked(launchOrcaApp).mockImplementationOnce(() => {
+      writeMetadata(userDataPath, endpoint, 'token', process.pid)
+    })
+
+    const client = new RuntimeClient(userDataPath, 100)
+
+    const failure = await client.openOrca(1_000).then(
+      () => null,
+      (error: unknown) => error as { code: string; message: string; data?: unknown }
+    )
+    expect(failure?.code).toBe('runtime_open_timeout')
+    expect(failure?.message).not.toContain('unreachable')
+    expect(failure?.data).toBeUndefined()
+    // The second timeout case: answers all the way through, just no window.
+    expect(failure?.message).toContain('is responding and still running headlessly')
+  })
+
   it('openOrca waits for a reachable headless runtime to expose a desktop window', async () => {
     const userDataPath = mkdtempSync(join(tmpdir(), 'orca-runtime-client-'))
     const endpoint = join(userDataPath, 'runtime.sock')
diff --git a/src/cli/runtime/client.ts b/src/cli/runtime/client.ts
index f9a855ae929..28bd6e08d82 100644
--- a/src/cli/runtime/client.ts
+++ b/src/cli/runtime/client.ts
@@ -9,6 +9,7 @@ import { parsePairingCode, type PairingOffer } from '../../shared/pairing'
 import { launchOrcaApp } from './launch'
 import { getDefaultUserDataPath, readMetadata } from './metadata'
 import { getCliStatus, projectRemoteAppStatus } from './status'
+import { describeOpenTimeout } from './runtime-open-timeout-reason'
 import { sendRequest } from './transport'
 import { RuntimeClientError, RuntimeRpcFailureError, type RuntimeRpcSuccess } from './types'
 import { attachMutationRecovery } from './client-error-recovery'
@@ -263,6 +264,13 @@ export class RuntimeClient {
     }
 
     const startedAt = Date.now()
+    // Why (STA-3969): the timeout must describe the NEWEST observation. A reason accumulated
+    // across polls outlives the poll that saw it and then gets reported as the current
+    // diagnosis -- first when the runtime recovered, and again when its process exited. So the
+    // loop keeps the latest status and the reason is read off that; the earlier one survives
+    // only as history, never as the live verdict.
+    let latest = initial.result
+    let lastObservedReason = initial.result.runtime.unreachableReason
     while (Date.now() - startedAt < timeoutMs) {
       const status = await this.getCliStatus()
       if (status.result.app.desktopWindowStatus === 'blocked') {
@@ -271,12 +279,24 @@ export class RuntimeClient {
       if (status.result.app.desktopWindowStatus === 'available') {
         return status
       }
+      latest = status.result
+      // A poll that ANSWERED resolves the earlier failure outright, so it is not even history
+      // any more; only an unresolved failure we can no longer diagnose is worth carrying.
+      lastObservedReason = latest.runtime.reachable
+        ? undefined
+        : (latest.runtime.unreachableReason ?? lastObservedReason)
       await delay(250)
     }
 
+    const currentReason = latest.runtime.unreachableReason
     throw new RuntimeClientError(
       'runtime_open_timeout',
-      'Timed out waiting for an Orca desktop window. The runtime may still be running headlessly.'
+      `Timed out waiting for an Orca desktop window${describeOpenTimeout(latest, lastObservedReason)}`,
+      currentReason
+        ? { unreachableReason: currentReason }
+        : lastObservedReason
+          ? { lastObservedUnreachableReason: lastObservedReason }
+          : undefined
     )
   }
 }
diff --git a/src/cli/runtime/local-runtime-unreachable-reason.test.ts b/src/cli/runtime/local-runtime-unreachable-reason.test.ts
new file mode 100644
index 00000000000..83fcc2cd9b1
--- /dev/null
+++ b/src/cli/runtime/local-runtime-unreachable-reason.test.ts
@@ -0,0 +1,111 @@
+import { describe, expect, it } from 'vitest'
+import type { RuntimeTransportMetadata } from '../../shared/runtime-bootstrap'
+import { classifyLocalRuntimeUnreachable } from './local-runtime-unreachable-reason'
+import { RuntimeClientError, RuntimeRpcFailureError, RuntimeTransportError } from './types'
+
+const PIPE: RuntimeTransportMetadata = {
+  kind: 'named-pipe',
+  endpoint: '\\\\.\\pipe\\orca-26272-abcd'
+}
+const SOCKET: RuntimeTransportMetadata = { kind: 'unix', endpoint: '/tmp/orca/o-1-ab.sock' }
+
+function connectError(osErrorCode: string | null): RuntimeTransportError {
+  return new RuntimeTransportError('runtime_unavailable', 'generic', 'connect', osErrorCode)
+}
+
+describe('classifyLocalRuntimeUnreachable', () => {
+  it.each([
+    ['ENOENT', 'endpoint_missing'],
+    ['EACCES', 'endpoint_permission_denied'],
+    ['EPERM', 'endpoint_permission_denied'],
+    ['ECONNREFUSED', 'connection_refused'],
+    ['ECONNRESET', 'connection_closed'],
+    ['EPIPE', 'connection_closed']
+  ] as const)('maps a %s connect failure to %s', (osErrorCode, expected) => {
+    const reason = classifyLocalRuntimeUnreachable(connectError(osErrorCode), PIPE, 1000)
+    expect(reason.code).toBe(expected)
+    expect(reason.osErrorCode).toBe(osErrorCode)
+  })
+
+  it('classifies a peer close by phase, not by an errno the OS never reported', () => {
+    const reason = classifyLocalRuntimeUnreachable(
+      new RuntimeTransportError('runtime_unavailable', 'closed', 'peer_closed'),
+      SOCKET,
+      1000
+    )
+    expect(reason.code).toBe('connection_closed')
+    expect(reason.osErrorCode).toBeUndefined()
+  })
+
+  it('maps a client-side timeout to request_timeout and names the budget', () => {
+    const reason = classifyLocalRuntimeUnreachable(
+      new RuntimeClientError('runtime_timeout', 'timed out'),
+      SOCKET,
+      1234
+    )
+    expect(reason.code).toBe('request_timeout')
+    expect(reason.message).toContain('1234ms')
+  })
+
+  it('maps an unreadable frame to invalid_response', () => {
+    const reason = classifyLocalRuntimeUnreachable(
+      new RuntimeClientError('invalid_runtime_response', 'bad frame'),
+      SOCKET,
+      1000
+    )
+    expect(reason.code).toBe('invalid_response')
+  })
+
+  // Why: a runtime that answers and declines is reachable. Routing it to a
+  // transport code would aim sandbox/permission advice at an auth failure.
+  it('quotes the runtime error when the runtime answers and refuses', () => {
+    const reason = classifyLocalRuntimeUnreachable(
+      new RuntimeRpcFailureError({
+        id: 'req',
+        ok: false,
+        error: { code: 'unauthorized', message: 'Auth token is not valid.' }
+      }),
+      SOCKET,
+      1000
+    )
+    expect(reason.code).toBe('request_rejected')
+    expect(reason.message).toContain('unauthorized')
+    expect(reason.message).toContain('Auth token is not valid.')
+  })
+
+  it('falls back to unknown without inventing a cause', () => {
+    const reason = classifyLocalRuntimeUnreachable(new Error('boom'), SOCKET, 1000)
+    expect(reason.code).toBe('unknown')
+    expect(reason.osErrorCode).toBeUndefined()
+  })
+
+  it('always reports the endpoint it actually tried, with the right noun', () => {
+    expect(classifyLocalRuntimeUnreachable(connectError('EACCES'), PIPE, 1000)).toMatchObject({
+      endpoint: PIPE.endpoint,
+      endpointKind: 'named-pipe'
+    })
+    expect(classifyLocalRuntimeUnreachable(connectError('EACCES'), PIPE, 1000).message).toContain(
+      'named pipe'
+    )
+    expect(classifyLocalRuntimeUnreachable(connectError('EACCES'), SOCKET, 1000).message).toContain(
+      'socket'
+    )
+  })
+
+  it('does not claim a permission-denied endpoint exists', () => {
+    const reason = classifyLocalRuntimeUnreachable(connectError('EACCES'), PIPE, 1000)
+
+    expect(reason.message).not.toMatch(/\bexists\b/i)
+    expect(reason.message).toContain('OS denied')
+  })
+
+  // The reported Windows 10 incident: the app process is alive, the pipe is not
+  // openable from this process. The guidance must name the isolation possibilities
+  // rather than telling the user to keep waiting.
+  it('offers session/sandbox guidance for a hidden Windows named pipe', () => {
+    const reason = classifyLocalRuntimeUnreachable(connectError('ENOENT'), PIPE, 1000)
+    expect(reason.message).toContain(PIPE.endpoint)
+    expect(reason.message).toMatch(/sandbox/i)
+    expect(reason.message).toMatch(/session/i)
+  })
+})
diff --git a/src/cli/runtime/local-runtime-unreachable-reason.ts b/src/cli/runtime/local-runtime-unreachable-reason.ts
new file mode 100644
index 00000000000..d5204d61e6b
--- /dev/null
+++ b/src/cli/runtime/local-runtime-unreachable-reason.ts
@@ -0,0 +1,100 @@
+import type {
+  CliRuntimeUnreachableCode,
+  CliRuntimeUnreachableReason
+} from '../../shared/runtime-types'
+import type { RuntimeTransportMetadata } from '../../shared/runtime-bootstrap'
+import { RuntimeClientError, RuntimeRpcFailureError, RuntimeTransportError } from './types'
+
+/**
+ * Why: STA-3969 — `orca status` used to swallow every local RPC failure and report
+ * `starting`, so a CLI that could not reach the runtime looked identical to one
+ * waiting on a runtime that was genuinely still coming up. The runtime publishes
+ * `orca-runtime.json` only *after* its transport is listening (RuntimeRpc.start),
+ * so once metadata names an endpoint, a failure to talk to that endpoint is never
+ * evidence of a start still in progress. Name the failure instead.
+ */
+export function classifyLocalRuntimeUnreachable(
+  error: unknown,
+  transport: RuntimeTransportMetadata,
+  timeoutMs: number
+): CliRuntimeUnreachableReason {
+  const endpoint = transport.endpoint
+  const endpointKind = transport.kind === 'named-pipe' ? 'named-pipe' : 'unix'
+  const noun = endpointKind === 'named-pipe' ? 'named pipe' : 'socket'
+  const osErrorCode = error instanceof RuntimeTransportError ? error.osErrorCode : null
+  const code = resolveCode(error, osErrorCode)
+  return {
+    code,
+    message:
+      code === 'request_rejected' && error instanceof RuntimeRpcFailureError
+        ? `The runtime at ${endpoint} answered but refused the status request (${error.response.error.code}): ${error.response.error.message}`
+        : describe(code, { endpoint, noun, timeoutMs }),
+    endpoint,
+    endpointKind,
+    ...(osErrorCode ? { osErrorCode } : {})
+  }
+}
+
+function resolveCode(error: unknown, osErrorCode: string | null): CliRuntimeUnreachableCode {
+  // Why: a runtime that answers and declines is not unreachable in the transport
+  // sense — keep it distinct so "fix your sandbox" advice never lands on an auth
+  // or version rejection.
+  if (error instanceof RuntimeRpcFailureError) {
+    return 'request_rejected'
+  }
+  if (error instanceof RuntimeTransportError && error.phase === 'peer_closed') {
+    return 'connection_closed'
+  }
+  switch (osErrorCode) {
+    case 'ENOENT':
+      return 'endpoint_missing'
+    case 'EACCES':
+    case 'EPERM':
+      return 'endpoint_permission_denied'
+    case 'ECONNREFUSED':
+      return 'connection_refused'
+    case 'EPIPE':
+    case 'ECONNRESET':
+      return 'connection_closed'
+    case null:
+    default:
+      break
+  }
+  if (error instanceof RuntimeClientError) {
+    if (error.code === 'runtime_timeout') {
+      return 'request_timeout'
+    }
+    if (error.code === 'invalid_runtime_response') {
+      return 'invalid_response'
+    }
+  }
+  return 'unknown'
+}
+
+// Why: every branch names the endpoint and states only what was observed. The
+// sandbox/session wording is a list of possibilities, not a verdict — the CLI
+// cannot see why the OS hid the endpoint, and must not claim it can.
+function describe(
+  code: CliRuntimeUnreachableCode,
+  ctx: { endpoint: string; noun: string; timeoutMs: number }
+): string {
+  const { endpoint, noun, timeoutMs } = ctx
+  switch (code) {
+    case 'endpoint_missing':
+      return `Orca published the ${noun} ${endpoint}, but it does not exist for this process. Either the runtime shut its endpoint down, or this process cannot see it — a sandbox, container, or different user session each hide it this way. Run the CLI as the same user and outside any sandbox, or restart Orca.`
+    case 'endpoint_permission_denied':
+      return `The OS denied this process access to the ${noun} ${endpoint}. Run the CLI as the same user that runs Orca, outside any sandbox that restricts ${noun} access.`
+    case 'connection_refused':
+      return `The ${noun} ${endpoint} refused the connection. Orca's runtime is most likely shutting down; restart Orca.`
+    case 'connection_closed':
+      return `Connected to ${endpoint}, but the runtime closed the connection before replying. It may be shutting down or at its connection limit; restart Orca.`
+    case 'request_timeout':
+      return `Connected to ${endpoint}, but the runtime did not reply within ${timeoutMs}ms. It is reachable and not answering, so it is busy or wedged rather than starting.`
+    case 'request_rejected':
+      return `The runtime at ${endpoint} answered but refused the status request.`
+    case 'invalid_response':
+      return `The runtime at ${endpoint} returned a response this CLI could not read. The CLI and the Orca app are most likely different versions; reinstall the CLI from this Orca build.`
+    case 'unknown':
+      return `Could not talk to the Orca runtime at ${endpoint}. The Orca app process is running, so this is not a start still in progress.`
+  }
+}
diff --git a/src/cli/runtime/local-runtime-unreachable-status.test.ts b/src/cli/runtime/local-runtime-unreachable-status.test.ts
new file mode 100644
index 00000000000..0d2f219250d
--- /dev/null
+++ b/src/cli/runtime/local-runtime-unreachable-status.test.ts
@@ -0,0 +1,185 @@
+import { mkdtempSync, writeFileSync } from 'node:fs'
+import { createServer, type Server, type Socket } from 'node:net'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterEach, describe, expect, it } from 'vitest'
+import { getRuntimeMetadataPath } from '../../shared/runtime-bootstrap'
+import { formatCliStatus } from '../format'
+import { RuntimeClient } from './client'
+
+const servers = new Set<Server>()
+const sockets = new Set<Socket>()
+
+afterEach(async () => {
+  for (const socket of sockets) {
+    socket.destroy()
+  }
+  sockets.clear()
+  await Promise.all(
+    [...servers].map((server) => new Promise<void>((resolve) => server.close(() => resolve())))
+  )
+  servers.clear()
+})
+
+function seedMetadata(endpoint: string, pid: number): string {
+  const userDataPath = mkdtempSync(join(tmpdir(), 'orca-unreachable-'))
+  writeFileSync(
+    getRuntimeMetadataPath(userDataPath),
+    JSON.stringify({
+      runtimeId: 'runtime-under-test',
+      pid,
+      transports: [{ kind: 'unix', endpoint }],
+      authToken: 'token',
+      startedAt: Date.now()
+    })
+  )
+  return userDataPath
+}
+
+async function listen(endpoint: string, onConnection: (socket: Socket) => void): Promise<void> {
+  const server = createServer((socket) => {
+    sockets.add(socket)
+    socket.once('close', () => sockets.delete(socket))
+    onConnection(socket)
+  })
+  servers.add(server)
+  await new Promise<void>((resolve) => server.listen(endpoint, resolve))
+}
+
+// Why: Windows publishes named pipes, which these Unix-socket fixtures cannot stand in for.
+// The classification itself is platform-independent and covered by the reason unit tests.
+describe.skipIf(process.platform === 'win32')('local runtime reachability status', () => {
+  // STA-3969: the reported incident. The Orca app process is alive and metadata
+  // names an endpoint, but the CLI cannot open it — reported for weeks as
+  // `starting`, which told the user to keep waiting for a start that had already
+  // happened. The runtime writes this metadata only after its transport is
+  // listening, so `starting` is never a truthful reading here.
+  it('names the missing endpoint instead of claiming the runtime is still starting', async () => {
+    const userDataPath = seedMetadata(
+      join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'gone.sock'),
+      process.pid
+    )
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.app).toMatchObject({ running: true, pid: process.pid })
+    expect(status.result.runtime.state).toBe('unreachable')
+    expect(status.result.runtime.reachable).toBe(false)
+    expect(status.result.graph.state).toBe('unreachable')
+    expect(status.result.runtime.unreachableReason).toMatchObject({
+      code: 'endpoint_missing',
+      osErrorCode: 'ENOENT'
+    })
+    expect(status.result.runtime.unreachableReason?.message).toContain('gone.sock')
+  })
+
+  it('reports a runtime that closes the connection before replying', async () => {
+    const endpoint = join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'closes.sock')
+    await listen(endpoint, (socket) => socket.destroy())
+    const userDataPath = seedMetadata(endpoint, process.pid)
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.state).toBe('unreachable')
+    expect(status.result.runtime.unreachableReason?.code).toBe('connection_closed')
+  })
+
+  // Why: `socket.destroy()` above surfaces as an ECONNRESET on the client's error
+  // handler. A clean FIN with no reply takes the separate 'close' path, which has
+  // no errno at all — it is classified by transport phase, so it needs its own case.
+  it('reports a runtime that half-closes cleanly without replying', async () => {
+    const endpoint = join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'fin.sock')
+    await listen(endpoint, (socket) => {
+      socket.once('data', () => socket.end())
+    })
+    const userDataPath = seedMetadata(endpoint, process.pid)
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.state).toBe('unreachable')
+    expect(status.result.runtime.unreachableReason).toMatchObject({ code: 'connection_closed' })
+    expect(status.result.runtime.unreachableReason?.osErrorCode).toBeUndefined()
+  })
+
+  it('reports a runtime that accepts the connection but never answers', async () => {
+    const endpoint = join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'silent.sock')
+    await listen(endpoint, () => {})
+    const userDataPath = seedMetadata(endpoint, process.pid)
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.state).toBe('unreachable')
+    expect(status.result.runtime.unreachableReason?.code).toBe('request_timeout')
+    expect(status.result.runtime.unreachableReason?.message).toContain('rather than starting')
+  })
+
+  it('separates a runtime that answers and refuses from one it cannot reach', async () => {
+    const endpoint = join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'refuses.sock')
+    await listen(endpoint, (socket) => {
+      socket.once('data', (data) => {
+        const request = JSON.parse(String(data).trim()) as { id: string }
+        socket.write(
+          `${JSON.stringify({
+            id: request.id,
+            ok: false,
+            error: { code: 'unauthorized', message: 'Auth token is not valid for this runtime.' },
+            _meta: { runtimeId: 'runtime-under-test' }
+          })}\n`
+        )
+      })
+    })
+    const userDataPath = seedMetadata(endpoint, process.pid)
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.unreachableReason?.code).toBe('request_rejected')
+    expect(status.result.runtime.unreachableReason?.message).toContain(
+      'Auth token is not valid for this runtime.'
+    )
+  })
+
+  // Preservation: a dead pid is still a stale bootstrap, not an unreachable runtime.
+  it('still reports a stale bootstrap when the recorded process is gone', async () => {
+    const userDataPath = seedMetadata(
+      join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'dead.sock'),
+      2 ** 30
+    )
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.state).toBe('stale_bootstrap')
+    expect(status.result.runtime.unreachableReason).toBeUndefined()
+    expect(status.result.app).toMatchObject({ running: false, pid: null })
+  })
+
+  // Why: the default `orca status` output is plain text, so the cause has to reach
+  // the non-JSON reader too — that is the surface the report was read from.
+  it('prints the cause in the plain-text status output', async () => {
+    const userDataPath = seedMetadata(
+      join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'gone.sock'),
+      process.pid
+    )
+
+    const text = formatCliStatus((await new RuntimeClient(userDataPath).getCliStatus()).result)
+
+    expect(text).toContain('runtimeState: unreachable')
+    expect(text).toContain('unreachableCode: endpoint_missing')
+    expect(text).toContain('unreachableDetail: ')
+    expect(text).toContain('gone.sock')
+  })
+
+  // Constraint: nothing may report a runtime as usable when it is not.
+  it('never reports a reachable or ready runtime while the endpoint is unusable', async () => {
+    const userDataPath = seedMetadata(
+      join(mkdtempSync(join(tmpdir(), 'orca-ep-')), 'gone.sock'),
+      process.pid
+    )
+
+    const status = await new RuntimeClient(userDataPath).getCliStatus()
+
+    expect(status.result.runtime.reachable).toBe(false)
+    expect(status.result.runtime.state).not.toBe('ready')
+    expect(status.result.runtime.runtimeId).toBeNull()
+    expect(status._meta?.runtimeId).toBe('none')
+  })
+})
diff --git a/src/cli/runtime/runtime-open-timeout-reason.test.ts b/src/cli/runtime/runtime-open-timeout-reason.test.ts
new file mode 100644
index 00000000000..c31d485f414
--- /dev/null
+++ b/src/cli/runtime/runtime-open-timeout-reason.test.ts
@@ -0,0 +1,102 @@
+import { describe, expect, it } from 'vitest'
+import { describeOpenTimeout } from './runtime-open-timeout-reason'
+import type { CliRuntimeUnreachableReason, CliStatusResult } from '../../shared/runtime-types'
+
+// Why: the poll loop can only feed this the states today's local producer happens to emit, so
+// driving it through the client leaves whole arms unpinned. Each arm is a promise about what
+// the message may claim, so each one is asserted against the status it describes (STA-3969).
+function status(overrides: {
+  appRunning: boolean
+  reachable: boolean
+  state: CliStatusResult['runtime']['state']
+  unreachableReason?: CliRuntimeUnreachableReason
+}): CliStatusResult {
+  return {
+    app: { running: overrides.appRunning, pid: overrides.appRunning ? 4242 : null },
+    runtime: {
+      state: overrides.state,
+      reachable: overrides.reachable,
+      runtimeId: overrides.reachable ? 'runtime-1' : null,
+      ...(overrides.unreachableReason ? { unreachableReason: overrides.unreachableReason } : {})
+    },
+    graph: { state: overrides.reachable ? 'ready' : 'unreachable' }
+  }
+}
+
+const history: CliRuntimeUnreachableReason = {
+  code: 'endpoint_missing',
+  message: 'Orca published the socket /tmp/never-listened.sock, but it does not exist.',
+  endpoint: '/tmp/never-listened.sock',
+  endpointKind: 'unix'
+}
+
+describe('describeOpenTimeout', () => {
+  it('reports the current reason as the live diagnosis', () => {
+    const text = describeOpenTimeout(
+      status({
+        appRunning: true,
+        reachable: false,
+        state: 'unreachable',
+        unreachableReason: history
+      }),
+      undefined
+    )
+    expect(text).toContain('the Orca app process is running but its runtime is unreachable')
+    expect(text).toContain(history.message)
+  })
+
+  it('calls a rejected request an answer, never unreachable', () => {
+    const text = describeOpenTimeout(
+      status({
+        appRunning: true,
+        reachable: false,
+        state: 'unreachable',
+        unreachableReason: { ...history, code: 'request_rejected', message: 'refused: bad token' }
+      }),
+      undefined
+    )
+    expect(text).toContain('answered but refused the status request')
+    expect(text).not.toContain('unreachable')
+  })
+
+  it('says the runtime answered when the newest poll was reachable', () => {
+    const text = describeOpenTimeout(
+      status({ appRunning: true, reachable: true, state: 'graph_not_ready' }),
+      history
+    )
+    expect(text).toContain('is responding and still running headlessly')
+    // A poll that answered resolves the earlier failure, so it is not even history any more.
+    expect(text).not.toContain(history.message)
+  })
+
+  // Why: this is the arm the client's own producer cannot currently reach, and dropping it makes
+  // the message claim no process is running while the pid is alive — the exact false report
+  // STA-3969 exists to stop.
+  it('never claims the process is gone while the newest status says it is running', () => {
+    const text = describeOpenTimeout(
+      status({ appRunning: true, reachable: false, state: 'graph_not_ready' }),
+      undefined
+    )
+    expect(text).toBe('. The runtime may still be running headlessly.')
+    expect(text).not.toContain('no longer running')
+    expect(text).not.toContain('No Orca runtime is running')
+  })
+
+  it('reports a dead app process without inheriting the old live verdict', () => {
+    const text = describeOpenTimeout(
+      status({ appRunning: false, reachable: false, state: 'stale_bootstrap' }),
+      history
+    )
+    expect(text).toContain('The Orca app process is no longer running.')
+    expect(text).toContain('The last failure it reported was:')
+    expect(text).not.toContain('but its runtime is unreachable')
+  })
+
+  it('says no runtime is running when none was ever published, with no history to add', () => {
+    const text = describeOpenTimeout(
+      status({ appRunning: false, reachable: false, state: 'not_running' }),
+      undefined
+    )
+    expect(text).toBe('. No Orca runtime is running.')
+  })
+})
diff --git a/src/cli/runtime/runtime-open-timeout-reason.ts b/src/cli/runtime/runtime-open-timeout-reason.ts
new file mode 100644
index 00000000000..29ceee4b8bc
--- /dev/null
+++ b/src/cli/runtime/runtime-open-timeout-reason.ts
@@ -0,0 +1,32 @@
+import type { CliRuntimeUnreachableReason, CliStatusResult } from '../../shared/runtime-types'
+
+// Why (STA-3969): the rule this enforces is that every clause names the observation it came
+// from. `unreachableReason` is produced in exactly one place -- the branch that checked the pid
+// and found the process alive -- so its presence is what licenses saying the process is running,
+// and its absence forbids it. A reason from an earlier poll is reported as history, tense marked,
+// never folded into the live verdict.
+export function describeOpenTimeout(
+  latest: CliStatusResult,
+  lastObservedReason: CliRuntimeUnreachableReason | undefined
+): string {
+  const current = latest.runtime.unreachableReason
+  if (current) {
+    // A rejected request is an answer, so it cannot also be described as unreachable.
+    return current.code === 'request_rejected'
+      ? `: the Orca runtime answered but refused the status request. ${current.message}`
+      : `: the Orca app process is running but its runtime is unreachable. ${current.message}`
+  }
+  if (latest.runtime.reachable) {
+    return '. The Orca runtime is responding and still running headlessly; it did not open a window in time.'
+  }
+  if (latest.app.running) {
+    return '. The runtime may still be running headlessly.'
+  }
+  const state =
+    latest.runtime.state === 'stale_bootstrap'
+      ? '. The Orca app process is no longer running.'
+      : '. No Orca runtime is running.'
+  return lastObservedReason
+    ? `${state} The last failure it reported was: ${lastObservedReason.message}`
+    : state
+}
diff --git a/src/cli/runtime/status.ts b/src/cli/runtime/status.ts
index e4a181a8d51..cbaf9e9c5b2 100644
--- a/src/cli/runtime/status.ts
+++ b/src/cli/runtime/status.ts
@@ -7,6 +7,9 @@ import {
   resolveDesktopWindowStatus
 } from '../../shared/cli-app-status-projection'
 import { RuntimeRpcFailureError, type RuntimeRpcSuccess } from './types'
+import { classifyLocalRuntimeUnreachable } from './local-runtime-unreachable-reason'
+
+const STATUS_REQUEST_TIMEOUT_MS = 1000
 
 export { projectRemoteAppStatus, resolveDesktopWindowStatus }
 
@@ -36,7 +39,12 @@ export async function getCliStatus(
   }
 
   try {
-    const response = await sendRequest<RuntimeStatus>(metadata, 'status.get', undefined, 1000)
+    const response = await sendRequest<RuntimeStatus>(
+      metadata,
+      'status.get',
+      undefined,
+      STATUS_REQUEST_TIMEOUT_MS
+    )
     if (response.ok === false) {
       throw new RuntimeRpcFailureError(response)
     }
@@ -63,21 +71,31 @@ export async function getCliStatus(
         state: graphState
       }
     })
-  } catch {
+  } catch (error) {
     const running = isProcessRunning(metadata.pid)
+    if (!running) {
+      return buildCliStatusResponse({
+        app: { running: false, pid: null },
+        runtime: { state: 'stale_bootstrap', reachable: false, runtimeId: null },
+        graph: { state: 'not_running' }
+      })
+    }
+    // Why: STA-3969 — metadata naming this endpoint is only written after the
+    // runtime's transport is listening, so a live app plus a failed request is a
+    // reachability failure, never a start in progress. Report the cause.
     return buildCliStatusResponse({
-      app: {
-        running,
-        pid: running ? metadata.pid : null
-      },
+      app: { running: true, pid: metadata.pid },
       runtime: {
-        state: running ? 'starting' : 'stale_bootstrap',
+        state: 'unreachable',
         reachable: false,
-        runtimeId: null
+        runtimeId: null,
+        unreachableReason: classifyLocalRuntimeUnreachable(
+          error,
+          transport,
+          STATUS_REQUEST_TIMEOUT_MS
+        )
       },
-      graph: {
-        state: running ? 'starting' : 'not_running'
-      }
+      graph: { state: 'unreachable' }
     })
   }
 }
diff --git a/src/cli/runtime/transport.ts b/src/cli/runtime/transport.ts
index 091ca9da0e0..82a43793f8d 100644
--- a/src/cli/runtime/transport.ts
+++ b/src/cli/runtime/transport.ts
@@ -3,7 +3,7 @@ import { randomUUID } from 'node:crypto'
 import { findTransport, type RuntimeMetadata } from '../../shared/runtime-bootstrap'
 import type { RuntimeOrchestrationEnvelope } from '../../shared/runtime-rpc-envelope'
 import { isKeepaliveFrame, RuntimeRpcEnvelopeSchema } from './envelope-schema'
-import { RuntimeClientError, type RuntimeRpcResponse } from './types'
+import { RuntimeClientError, RuntimeTransportError, type RuntimeRpcResponse } from './types'
 import { MAX_TIMER_DELAY_MS, isSafeTimerDelayMs } from '../../shared/timer-delay'
 
 export async function sendRequest<TResult>(
@@ -66,12 +66,17 @@ export async function sendRequest<TResult>(
     }
 
     socket.setEncoding('utf8')
-    socket.once('error', () => {
+    // Why: STA-3969 — the errno is the whole diagnosis (ENOENT = endpoint gone,
+    // EACCES = visible but barred), so keep it instead of collapsing every
+    // connect failure into one message the caller cannot act on.
+    socket.once('error', (error: NodeJS.ErrnoException) => {
       finish({
         ok: false,
-        error: new RuntimeClientError(
+        error: new RuntimeTransportError(
           'runtime_unavailable',
-          'Could not connect to the running Orca app. Restart Orca and try again.'
+          'Could not connect to the running Orca app. Restart Orca and try again.',
+          'connect',
+          error.code ?? null
         )
       })
     })
@@ -82,9 +87,10 @@ export async function sendRequest<TResult>(
     socket.once('close', () => {
       finish({
         ok: false,
-        error: new RuntimeClientError(
+        error: new RuntimeTransportError(
           'runtime_unavailable',
-          'The Orca runtime closed the connection before responding. Restart Orca and try again.'
+          'The Orca runtime closed the connection before responding. Restart Orca and try again.',
+          'peer_closed'
         )
       })
     })
diff --git a/src/cli/runtime/types.ts b/src/cli/runtime/types.ts
index a15515acfdb..c38b1d5bd4f 100644
--- a/src/cli/runtime/types.ts
+++ b/src/cli/runtime/types.ts
@@ -20,6 +20,28 @@ export class RuntimeClientError extends Error {
   }
 }
 
+// Why: STA-3969 — both of these failures share the `runtime_unavailable` code, and
+// the errno is the only thing separating "the endpoint is gone" (ENOENT) from "this
+// process may not open it" (EACCES). Carry the phase and the errno so callers can
+// classify instead of guessing. osErrorCode stays null when the OS reported none.
+export type RuntimeTransportPhase = 'connect' | 'peer_closed'
+
+export class RuntimeTransportError extends RuntimeClientError {
+  readonly phase: RuntimeTransportPhase
+  readonly osErrorCode: string | null
+
+  constructor(
+    code: string,
+    message: string,
+    phase: RuntimeTransportPhase,
+    osErrorCode: string | null = null
+  ) {
+    super(code, message)
+    this.phase = phase
+    this.osErrorCode = osErrorCode
+  }
+}
+
 export class RuntimeRpcFailureError extends RuntimeClientError {
   readonly response: RuntimeRpcFailure
 
diff --git a/src/shared/runtime-client-export-parity.test.ts b/src/shared/runtime-client-export-parity.test.ts
index 2b86d2e6e99..bd9db429b34 100644
--- a/src/shared/runtime-client-export-parity.test.ts
+++ b/src/shared/runtime-client-export-parity.test.ts
@@ -68,6 +68,8 @@ type RuntimeTypeInventory = [
   Runtime.BrowserViewportResult,
   Runtime.BrowserWaitResult,
   Runtime.CliRuntimeState,
+  Runtime.CliRuntimeUnreachableCode,
+  Runtime.CliRuntimeUnreachableReason,
   Runtime.CliStatusResult,
   Runtime.ComputerActionMetadata,
   Runtime.ComputerActionResult,
diff --git a/src/shared/runtime-session-contracts.ts b/src/shared/runtime-session-contracts.ts
index 1249870c548..add5e2967df 100644
--- a/src/shared/runtime-session-contracts.ts
+++ b/src/shared/runtime-session-contracts.ts
@@ -100,6 +100,28 @@ export type CliRuntimeState =
   | 'ready'
   | 'graph_not_ready'
   | 'stale_bootstrap'
+  // Why: STA-3969 — the CLI reached a definite failure talking to a published
+  // endpoint. Per docs/reference/ssh-execution-boundary.md a socket that failed
+  // is not an observation of the runtime, so it may not be reported as 'starting'.
+  | 'unreachable'
+
+export type CliRuntimeUnreachableCode =
+  | 'endpoint_missing'
+  | 'endpoint_permission_denied'
+  | 'connection_refused'
+  | 'connection_closed'
+  | 'request_timeout'
+  | 'request_rejected'
+  | 'invalid_response'
+  | 'unknown'
+
+export type CliRuntimeUnreachableReason = {
+  code: CliRuntimeUnreachableCode
+  message: string
+  endpoint: string
+  endpointKind: 'unix' | 'named-pipe'
+  osErrorCode?: string
+}
 
 export type CliStatusResult = {
   target?: { kind: 'local' } | { kind: 'environment'; environment: string }
@@ -116,9 +138,12 @@ export type CliStatusResult = {
     remoteUpdateSupport?: RemoteServerUpdateSupport
     capabilities?: RuntimeCapability[]
     degradations?: RuntimeDegradation[]
+    // Why: present exactly when state is 'unreachable' — the cause is the whole
+    // point of the state, and without it the caller is back to guessing.
+    unreachableReason?: CliRuntimeUnreachableReason
   }
   graph: {
-    state: RuntimeGraphStatus | 'not_running' | 'starting'
+    state: RuntimeGraphStatus | 'not_running' | 'starting' | 'unreachable'
   }
 }
 
diff --git a/src/shared/runtime-types.ts b/src/shared/runtime-types.ts
index 856268217aa..b16d8fd1120 100644
--- a/src/shared/runtime-types.ts
+++ b/src/shared/runtime-types.ts
@@ -109,6 +109,8 @@ export type {
 } from './runtime-capability-degradation'
 export type {
   CliRuntimeState,
+  CliRuntimeUnreachableCode,
+  CliRuntimeUnreachableReason,
   CliStatusResult,
   DeviceScope,
   RuntimeBrowserDriverState,