diff --git a/packages/sim-cli/src/auth/device-flow.ts b/packages/sim-cli/src/auth/device-flow.ts
index 84dfaf3c2ba..1c72a2e9f34 100644
--- a/packages/sim-cli/src/auth/device-flow.ts
+++ b/packages/sim-cli/src/auth/device-flow.ts
@@ -1,6 +1,7 @@
 import { createHash, randomBytes, randomInt } from 'node:crypto'
 import { sleep } from '../helpers'
 import { REDIRECT_STATUSES, redirectEndpoint, SimApiError } from '../http/client'
+import { USER_AGENT } from '../version'
 
 /**
  * The terminal half of the CLI key handoff.
@@ -167,7 +168,11 @@ export async function pollForKey(
     try {
       response = await fetch(new URL(POLL_PATH, endpoint), {
         method: 'POST',
-        headers: { 'content-type': 'application/json', accept: 'application/json' },
+        headers: {
+          'content-type': 'application/json',
+          accept: 'application/json',
+          'user-agent': USER_AGENT,
+        },
         body: JSON.stringify({ request: auth.request, verifier: auth.pollSecret }),
         signal,
         redirect: 'manual',
diff --git a/packages/sim-cli/src/http/client.test.ts b/packages/sim-cli/src/http/client.test.ts
index eb56855742b..dc965b2e9e0 100644
--- a/packages/sim-cli/src/http/client.test.ts
+++ b/packages/sim-cli/src/http/client.test.ts
@@ -1,6 +1,7 @@
 import { afterEach, describe, expect, it, vi } from 'vitest'
 import { CLI_CONTRACT } from '../contract/commands'
 import { V2_OPERATIONS, type V2OperationName } from '../generated/v2-api'
+import { USER_AGENT } from '../version'
 import {
   formatApiErrorDetails,
   redirectEndpoint,
@@ -313,6 +314,29 @@ describe('non-JSON responses', () => {
   })
 })
 
+describe('request identity', () => {
+  it('identifies the CLI, its version and its runtime to the API', async () => {
+    // Without a User-Agent a CLI request is indistinguishable from any other
+    // API traffic, so a bug that only reproduces on one version cannot be found
+    // in the server's own logs.
+    const fetchMock = vi.fn().mockResolvedValue(
+      new Response(JSON.stringify({ data: [] }), {
+        status: 200,
+        headers: { 'content-type': 'application/json' },
+      })
+    )
+    vi.stubGlobal('fetch', fetchMock)
+
+    await client().request('/api/v2/workflows')
+
+    const headers = fetchMock.mock.calls[0][1].headers as Record<string, string>
+    expect(headers['user-agent']).toBe(USER_AGENT)
+    expect(USER_AGENT).toMatch(/^sim-cli\/\d+\.\d+\.\d+/)
+    expect(USER_AGENT).toContain(`node/${process.versions.node}`)
+    expect(USER_AGENT).toContain(process.platform)
+  })
+})
+
 describe('personal-key-only operations', () => {
   it('appends the remedy, keyed off the code the API actually nests', async () => {
     // The envelope this asserts is the one staging returns: `error.code` is the
@@ -341,6 +365,34 @@ describe('personal-key-only operations', () => {
     })
   })
 
+  it('also recognises the principal-kind refusal, whose message is written for a log', async () => {
+    // The same refusal is raised at two layers under two codes. The
+    // principal-kind one answers "Principal kind workspace_api_key cannot
+    // perform operation audit_logs.list" — accurate, and useless to a reader
+    // who has no way to act on it. Recognising only the other code left every
+    // audit-log command stating the problem in server vocabulary with no remedy.
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue(
+        new Response(
+          JSON.stringify({
+            error: {
+              code: 'FORBIDDEN',
+              message: 'Principal kind workspace_api_key cannot perform operation audit_logs.list',
+              details: { code: 'PRINCIPAL_KIND_NOT_PERMITTED' },
+            },
+          }),
+          { status: 403, headers: { 'content-type': 'application/json' } }
+        )
+      )
+    )
+
+    await expect(client().request('/api/v2/audit-logs')).rejects.toMatchObject({
+      message:
+        'Principal kind workspace_api_key cannot perform operation audit_logs.list — this operation needs a personal API key: sim login --profile default',
+    })
+  })
+
   it('invents no remedy for other forbidden codes', async () => {
     vi.stubGlobal(
       'fetch',
diff --git a/packages/sim-cli/src/http/client.ts b/packages/sim-cli/src/http/client.ts
index 65f0ed120f3..d7531971b3a 100644
--- a/packages/sim-cli/src/http/client.ts
+++ b/packages/sim-cli/src/http/client.ts
@@ -1,5 +1,6 @@
 import chalk from 'chalk'
 import type { ResolvedProfile } from '../config/index'
+import { USER_AGENT } from '../version'
 
 /**
  * A failure the CLI can explain. Anything thrown as a `SimApiError` is printed
@@ -75,8 +76,21 @@ export const REDIRECT_STATUSES = new Set([301, 302, 303, 307, 308])
 /** Markup a JSON endpoint would never answer with — a proxy or landing page. */
 const MARKUP_PREFIX = /^\s*<(?:!doctype|html|\?xml)/i
 
-/** The one 403 cause the CLI can turn into an instruction. */
-const WORKSPACE_KEY_REFUSAL = 'WORKSPACE_KEY_OPERATION_NOT_PERMITTED'
+/**
+ * The 403 causes the CLI can turn into an instruction.
+ *
+ * Two codes describe the same refusal because they are raised at different
+ * layers: the workspace-key policy answers `WORKSPACE_KEY_OPERATION_NOT_PERMITTED`,
+ * while the principal-kind check answers `PRINCIPAL_KIND_NOT_PERMITTED` with a
+ * message written for a server log ("Principal kind workspace_api_key cannot
+ * perform operation audit_logs.list"). Recognising only the first left the
+ * audit-log commands stating the refusal in vocabulary the reader has no way to
+ * act on, and without the one sentence that resolves it.
+ */
+const KEY_SCOPE_REFUSALS = new Set([
+  'WORKSPACE_KEY_OPERATION_NOT_PERMITTED',
+  'PRINCIPAL_KIND_NOT_PERMITTED',
+])
 
 /**
  * Names the response the server actually sent, for a body that is not JSON.
@@ -156,8 +170,8 @@ function truncate(value: string, max: number): string {
 }
 
 /**
- * The refusal a workspace-scoped key gets from an operation only a personal key
- * may perform.
+ * Whether this is the refusal a workspace-scoped key gets from an operation only
+ * a personal key may perform, under either code that expresses it.
  *
  * `error.code` is the envelope's status class and is plain `FORBIDDEN` here; the
  * actionable code rides in `error.details.code`, which is where the v2 error
@@ -165,11 +179,12 @@ function truncate(value: string, max: number): string {
  * code meant the remedy was never appended against the real API. The top level
  * is still accepted so a server that promotes the code stays covered.
  */
-function namesWorkspaceKeyRefusal(error: SimApiError): boolean {
-  if (error.code === WORKSPACE_KEY_REFUSAL) return true
+function namesKeyScopeRefusal(error: SimApiError): boolean {
+  if (typeof error.code === 'string' && KEY_SCOPE_REFUSALS.has(error.code)) return true
   const details = error.details
   if (!details || typeof details !== 'object') return false
-  return (details as { code?: unknown }).code === WORKSPACE_KEY_REFUSAL
+  const code = (details as { code?: unknown }).code
+  return typeof code === 'string' && KEY_SCOPE_REFUSALS.has(code)
 }
 
 interface DetailIssue {
@@ -342,6 +357,7 @@ export class SimClient {
         headers: {
           ...(apiKey ? { 'x-api-key': apiKey } : {}),
           accept: 'application/json',
+          'user-agent': USER_AGENT,
           ...(hasBody ? { 'content-type': 'application/json' } : {}),
           ...options.headers,
         },
@@ -367,7 +383,7 @@ export class SimClient {
       if (response.status === 401) {
         error.message = `${error.message} — run: sim login --profile ${this.profile.name}`
       }
-      if (namesWorkspaceKeyRefusal(error)) {
+      if (namesKeyScopeRefusal(error)) {
         error.message = `${error.message} — this operation needs a personal API key: sim login --profile ${this.profile.name}`
       }
       throw error
diff --git a/packages/sim-cli/src/program.ts b/packages/sim-cli/src/program.ts
index c4de9012f2b..249de03fa1a 100644
--- a/packages/sim-cli/src/program.ts
+++ b/packages/sim-cli/src/program.ts
@@ -1,4 +1,3 @@
-import { readFileSync } from 'node:fs'
 import { Command, Option } from 'commander'
 import { loginCommand, logoutCommand, profilesCommand, whoamiCommand } from './commands/auth'
 import { configureCommand } from './commands/configure'
@@ -7,6 +6,7 @@ import { attachProtocolCommands } from './commands/protocol/index'
 import { attachSecretCommands } from './commands/secrets'
 import { OUTPUT_FORMATS } from './config/index'
 import { buildGeneratedCommands } from './runtime/build'
+import { CLI_VERSION } from './version'
 
 /** Root program description, shared by `--help` and the generated docs. */
 export const PROGRAM_DESCRIPTION = 'Talk to the Sim API from your terminal'
@@ -28,21 +28,6 @@ Examples:
   $ sim whoami --profile dev
 `
 
-function readPackageVersion(): string {
-  const metadata: unknown = JSON.parse(
-    readFileSync(new URL('../package.json', import.meta.url), 'utf8')
-  )
-  if (
-    typeof metadata !== 'object' ||
-    metadata === null ||
-    !('version' in metadata) ||
-    typeof metadata.version !== 'string'
-  ) {
-    throw new Error('CLI package metadata is missing a valid version')
-  }
-  return metadata.version
-}
-
 /**
  * Assemble the complete command tree.
  *
@@ -60,7 +45,7 @@ export function buildProgram(options: { version?: boolean } = {}): Command {
 
   program.name('sim').description(PROGRAM_DESCRIPTION)
 
-  if (options.version !== false) program.version(readPackageVersion())
+  if (options.version !== false) program.version(CLI_VERSION)
 
   program
     .option('-P, --profile <name>', 'Profile to use (env: SIM_PROFILE)')
diff --git a/packages/sim-cli/src/version.ts b/packages/sim-cli/src/version.ts
new file mode 100644
index 00000000000..bded74c6a93
--- /dev/null
+++ b/packages/sim-cli/src/version.ts
@@ -0,0 +1,41 @@
+import { readFileSync } from 'node:fs'
+
+/**
+ * The published package version, and the `User-Agent` built from it.
+ *
+ * Its own module because both the command tree and the HTTP client need the
+ * version, and the client cannot reach `program.ts` — `program` builds the
+ * commands, which reach the client, so importing it back would close a cycle.
+ *
+ * Read from `package.json` rather than inlined so a release cannot ship a
+ * version string that disagrees with the package it came from. The bundle keeps
+ * `dist/index.js` one directory below the manifest, and npm always publishes the
+ * manifest, so the relative path holds for an installed package as well as a
+ * local build.
+ */
+function readPackageVersion(): string {
+  const metadata: unknown = JSON.parse(
+    readFileSync(new URL('../package.json', import.meta.url), 'utf8')
+  )
+  if (
+    typeof metadata !== 'object' ||
+    metadata === null ||
+    !('version' in metadata) ||
+    typeof metadata.version !== 'string'
+  ) {
+    throw new Error('CLI package metadata is missing a valid version')
+  }
+  return metadata.version
+}
+
+export const CLI_VERSION = readPackageVersion()
+
+/**
+ * Identifies the CLI to the API, the way every other terminal client does.
+ *
+ * Without it a CLI request is indistinguishable from any other API traffic, so
+ * a bug that only reproduces on one CLI version cannot be found in the server's
+ * own logs. The runtime and platform ride along for the same reason: they are
+ * the first things asked about a transport failure that only some users see.
+ */
+export const USER_AGENT = `sim-cli/${CLI_VERSION} node/${process.versions.node} (${process.platform}; ${process.arch})`