diff --git a/packages/cli/src/cli-program.ts b/packages/cli/src/cli-program.ts
index 6359d897..07010f07 100644
--- a/packages/cli/src/cli-program.ts
+++ b/packages/cli/src/cli-program.ts
@@ -2,6 +2,7 @@ import { existsSync } from 'node:fs';
 import { join } from 'node:path';
 import { Command, type CommandUnknownOpts, InvalidArgumentError } from '@commander-js/extra-typings';
 import type { KtxCliDeps, KtxCliIo, KtxCliPackageInfo } from './cli-runtime.js';
+import { SLACK_HELP_FOOTER, writeErrorCommunityHint } from './community-cta.js';
 import { registerCompletionCommands } from './commands/completion-commands.js';
 import { registerConnectionCommands } from './commands/connection-commands.js';
 import { registerIngestCommands } from './commands/ingest-commands.js';
@@ -258,6 +259,7 @@ function createBaseProgram(info: KtxCliPackageInfo, io: KtxCliIo): Command {
     .helpOption('-h, --help', 'Show this help text')
     .configureHelp({ showGlobalOptions: true })
     .showHelpAfterError()
+    .addHelpText('after', `\n${SLACK_HELP_FOOTER}`)
     .exitOverride()
     .configureOutput({
       writeOut: (chunk) => io.stdout.write(chunk),
@@ -561,6 +563,7 @@ export async function runCommanderKtxCli(
           io,
         });
         io.stderr.write(`${formatCliError(error)}\n`);
+        writeErrorCommunityHint(io, 'error');
         return 1;
       }
     }
@@ -585,6 +588,7 @@ export async function runCommanderKtxCli(
       exitCode = error.exitCode === 0 ? 0 : 1;
     } else {
       io.stderr.write(`${formatCliError(error)}\n`);
+      writeErrorCommunityHint(io, 'error');
       exitCode = 1;
     }
   } finally {
diff --git a/packages/cli/src/cli-runtime.ts b/packages/cli/src/cli-runtime.ts
index 4e13b472..69416006 100644
--- a/packages/cli/src/cli-runtime.ts
+++ b/packages/cli/src/cli-runtime.ts
@@ -12,6 +12,7 @@ import type { KtxSqlArgs } from './sql.js';
 import { profileMark, profileSpan } from './startup-profile.js';
 import type { KtxTextIngestArgs } from './text-ingest.js';
 import { assertCliVersion } from './release-version.js';
+import { writeErrorCommunityHint } from './community-cta.js';
 
 profileMark('module:cli-runtime');
 
@@ -144,6 +145,16 @@ export function createGlobalExceptionReporter(io: KtxCliIo, info: KtxCliPackageI
   };
 }
 
+/** @internal */
+export function writeGlobalExceptionToStderr(io: KtxCliIo, error: unknown): void {
+  if (error instanceof Error && error.stack) {
+    io.stderr.write(`${error.stack}\n`);
+  } else {
+    io.stderr.write(`${String(error)}\n`);
+  }
+  writeErrorCommunityHint(io, 'crash');
+}
+
 export function installGlobalExceptionHandlers(io: KtxCliIo, info: KtxCliPackageInfo): () => void {
   const report = createGlobalExceptionReporter(io, info);
   const handle = (source: 'uncaughtException' | 'unhandledRejection', error: unknown): void => {
@@ -153,11 +164,7 @@ export function installGlobalExceptionHandlers(io: KtxCliIo, info: KtxCliPackage
       } catch {
         // Best-effort: preserve Node's process termination behavior.
       }
-      if (error instanceof Error && error.stack) {
-        io.stderr.write(`${error.stack}\n`);
-      } else {
-        io.stderr.write(`${String(error)}\n`);
-      }
+      writeGlobalExceptionToStderr(io, error);
       process.exit(1);
     })();
   };
diff --git a/packages/cli/src/community-cta.ts b/packages/cli/src/community-cta.ts
new file mode 100644
index 00000000..b4702542
--- /dev/null
+++ b/packages/cli/src/community-cta.ts
@@ -0,0 +1,28 @@
+import type { KtxCliIo } from './cli-runtime.js';
+import { isWritableTtyOutput } from './io/tty.js';
+import { dim } from './io/symbols.js';
+import { SLACK_URL } from './links.js';
+
+type ErrorCtaVariant = 'error' | 'crash';
+
+/** @internal */
+export const SLACK_HELP_FOOTER = `Community & support: ${SLACK_URL}`;
+
+/** @internal */
+export const SLACK_SETUP_NOTE = {
+  title: 'Community',
+  body: `Questions or feedback? Join the ktx Slack: ${SLACK_URL}`,
+} as const;
+
+export function writeErrorCommunityHint(io: KtxCliIo, variant: ErrorCtaVariant): void {
+  if (!isWritableTtyOutput(io.stderr)) {
+    return;
+  }
+
+  const line =
+    variant === 'crash'
+      ? `This may be a bug - report it or ask in the ktx community: ${SLACK_URL}`
+      : `Stuck? The ktx community can help: ${SLACK_URL}`;
+
+  io.stderr.write(`${dim(line)}\n`);
+}
diff --git a/packages/cli/src/io/tty.ts b/packages/cli/src/io/tty.ts
new file mode 100644
index 00000000..43467d4e
--- /dev/null
+++ b/packages/cli/src/io/tty.ts
@@ -0,0 +1,17 @@
+import type { Writable } from 'node:stream';
+
+import type { KtxCliIo } from '../cli-runtime.js';
+
+type KtxCliOutput = (KtxCliIo['stdout'] | KtxCliIo['stderr']) & {
+  isTTY?: boolean;
+  columns?: number;
+  on?: unknown;
+};
+
+export function isWritableTtyOutput(output: KtxCliOutput): output is KtxCliOutput & Writable {
+  return (
+    (output as { isTTY?: unknown }).isTTY === true &&
+    typeof (output as { on?: unknown }).on === 'function' &&
+    typeof (output as { columns?: unknown }).columns !== 'undefined'
+  );
+}
diff --git a/packages/cli/src/links.ts b/packages/cli/src/links.ts
new file mode 100644
index 00000000..1ca62c59
--- /dev/null
+++ b/packages/cli/src/links.ts
@@ -0,0 +1 @@
+export const SLACK_URL = 'https://ktx.sh/slack';
diff --git a/packages/cli/src/setup-agents.ts b/packages/cli/src/setup-agents.ts
index a671ba4b..3c7e5bad 100644
--- a/packages/cli/src/setup-agents.ts
+++ b/packages/cli/src/setup-agents.ts
@@ -1,7 +1,6 @@
 import { existsSync } from 'node:fs';
 import { mkdir, readFile, rm, writeFile } from 'node:fs/promises';
 import { dirname, join, relative, resolve } from 'node:path';
-import type { Writable } from 'node:stream';
 import { fileURLToPath } from 'node:url';
 import { styleText } from 'node:util';
 import { log, outro } from '@clack/prompts';
@@ -11,6 +10,7 @@ import { serializeKtxProjectConfig } from './context/project/config.js';
 import { strToU8, zipSync } from 'fflate';
 import type { KtxCliIo } from './cli-runtime.js';
 import { errorMessage, writePrefixedLines } from './clack.js';
+import { isWritableTtyOutput } from './io/tty.js';
 import {
   createKtxSetupPromptAdapter,
   createKtxSetupUiAdapter,
@@ -84,14 +84,6 @@ interface KtxCliLauncher {
   args: string[];
 }
 
-function isWritableTtyOutput(output: KtxCliIo['stdout']): output is KtxCliIo['stdout'] & Writable {
-  return (
-    output.isTTY === true &&
-    typeof (output as { on?: unknown }).on === 'function' &&
-    typeof (output as { columns?: unknown }).columns !== 'undefined'
-  );
-}
-
 function writeSetupInfo(io: KtxCliIo, message: string): void {
   if (isWritableTtyOutput(io.stdout)) {
     log.info(message, { output: io.stdout });
diff --git a/packages/cli/src/setup-prompts.ts b/packages/cli/src/setup-prompts.ts
index e508d8ff..e135004f 100644
--- a/packages/cli/src/setup-prompts.ts
+++ b/packages/cli/src/setup-prompts.ts
@@ -1,4 +1,3 @@
-import type { Writable } from 'node:stream';
 import {
   autocomplete,
   autocompleteMultiselect,
@@ -13,6 +12,7 @@ import {
   text,
 } from '@clack/prompts';
 import type { KtxCliIo } from './cli-runtime.js';
+import { isWritableTtyOutput } from './io/tty.js';
 import { withMenuOptionsSpacing, withTextInputNavigation } from './prompt-navigation.js';
 import { revealPassword } from './reveal-password-prompt.js';
 import { withSetupInterruptConfirmation } from './setup-interrupt.js';
@@ -211,14 +211,6 @@ export interface KtxSetupUiAdapter {
   note(message: string, title: string, io: KtxCliIo, options?: KtxSetupNoteOptions): void;
 }
 
-function isWritableTtyOutput(output: KtxCliIo['stdout']): output is KtxCliIo['stdout'] & Writable {
-  return (
-    output.isTTY === true &&
-    typeof (output as { on?: unknown }).on === 'function' &&
-    typeof (output as { columns?: unknown }).columns !== 'undefined'
-  );
-}
-
 export function createKtxSetupUiAdapter(): KtxSetupUiAdapter {
   return {
     intro(title, io) {
diff --git a/packages/cli/src/setup.ts b/packages/cli/src/setup.ts
index 9539a248..2ff58dbf 100644
--- a/packages/cli/src/setup.ts
+++ b/packages/cli/src/setup.ts
@@ -6,6 +6,7 @@ import { ktxLocalStateDbPath } from './context/project/local-state-db.js';
 import { loadKtxProject, type KtxLocalProject } from './context/project/project.js';
 import { readKtxSetupState } from './context/project/setup-config.js';
 import { getKtxCliPackageInfo, type KtxCliIo } from './cli-runtime.js';
+import { SLACK_SETUP_NOTE } from './community-cta.js';
 import { formatNextStepLines, formatSetupNextStepLines } from './next-steps.js';
 import { runtimeInstallPolicyFromFlags } from './managed-python-command.js';
 import { readManagedPythonRuntimeStatus } from './managed-python-runtime.js';
@@ -921,5 +922,6 @@ async function runKtxSetupInner(args: KtxSetupArgs, io: KtxCliIo, deps: KtxSetup
       );
     }
   }
+  setupUi.note(SLACK_SETUP_NOTE.body, SLACK_SETUP_NOTE.title, io);
   return 0;
 }
diff --git a/packages/cli/test/cli-program-telemetry.test.ts b/packages/cli/test/cli-program-telemetry.test.ts
index 30e2bd2b..fb624c66 100644
--- a/packages/cli/test/cli-program-telemetry.test.ts
+++ b/packages/cli/test/cli-program-telemetry.test.ts
@@ -13,9 +13,27 @@ vi.mock('../src/telemetry/exception.js', () => ({
   reportException: reportExceptionMock,
 }));
 
-function makeIo(stdoutIsTTY = true): { io: KtxCliIo; stdout: () => string; stderr: () => string } {
+function makeIo(
+  stdoutIsTTY = true,
+  stderrIsTTY = false,
+): { io: KtxCliIo; stdout: () => string; stderr: () => string } {
   let stdout = '';
   let stderr = '';
+  const stderrStream = stderrIsTTY
+    ? {
+        isTTY: true,
+        columns: 80,
+        on: () => undefined,
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      }
+    : {
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      };
+
   return {
     io: {
       stdout: {
@@ -24,11 +42,7 @@ function makeIo(stdoutIsTTY = true): { io: KtxCliIo; stdout: () => string; stder
           stdout += chunk;
         },
       },
-      stderr: {
-        write: (chunk) => {
-          stderr += chunk;
-        },
-      },
+      stderr: stderrStream,
     },
     stdout: () => stdout,
     stderr: () => stderr,
@@ -164,4 +178,75 @@ describe('runCommanderKtxCli telemetry', () => {
       }),
     );
   });
+
+  it('prints the Slack hint for unexpected command errors on TTY stderr only', async () => {
+    const ttyIo = makeIo(true, true);
+    const deps: KtxCliDeps = {
+      doctor: async () => {
+        throw new Error('status failed');
+      },
+    };
+
+    await expect(
+      runCommanderKtxCli(
+        ['--project-dir', tempDir, 'status', '--json'],
+        ttyIo.io,
+        deps,
+        info,
+        { runInit: async () => 0 },
+      ),
+    ).resolves.toBe(1);
+
+    expect(ttyIo.stderr()).toContain('status failed');
+    expect(ttyIo.stderr()).toContain('Stuck? The ktx community can help');
+    expect(ttyIo.stderr()).toContain('https://ktx.sh/slack');
+
+    const pipeIo = makeIo(true, false);
+    await expect(
+      runCommanderKtxCli(
+        ['--project-dir', tempDir, 'status', '--json'],
+        pipeIo.io,
+        deps,
+        info,
+        { runInit: async () => 0 },
+      ),
+    ).resolves.toBe(1);
+
+    expect(pipeIo.stderr()).toContain('status failed');
+    expect(pipeIo.stderr()).not.toContain('https://ktx.sh/slack');
+  });
+
+  it('does not print the Slack hint for Commander usage errors', async () => {
+    const io = makeIo(true, true);
+
+    await expect(
+      runCommanderKtxCli(['--not-a-real-option'], io.io, {}, info, { runInit: async () => 0 }),
+    ).resolves.toBe(1);
+
+    expect(io.stderr()).toContain("unknown option '--not-a-real-option'");
+    expect(io.stderr()).not.toContain('Stuck? The ktx community can help');
+  });
+
+  it('prints the Slack hint for bare interactive setup failures on TTY stderr', async () => {
+    const originalCwd = process.cwd();
+    const noProjectDir = await mkdtemp(join(tmpdir(), 'ktx-cli-bare-'));
+    const io = makeIo(true, true);
+    const deps: KtxCliDeps = {
+      setup: async () => {
+        throw new Error('setup failed');
+      },
+    };
+
+    try {
+      process.chdir(noProjectDir);
+      await expect(runCommanderKtxCli([], io.io, deps, info, { runInit: async () => 0 })).resolves.toBe(1);
+    } finally {
+      process.chdir(originalCwd);
+      await rm(noProjectDir, { recursive: true, force: true });
+    }
+
+    expect(io.stderr()).toContain('setup failed');
+    expect(io.stderr()).toContain('Stuck? The ktx community can help');
+    expect(io.stderr()).toContain('https://ktx.sh/slack');
+  });
 });
diff --git a/packages/cli/test/cli-program.test.ts b/packages/cli/test/cli-program.test.ts
index 332645aa..39c9955c 100644
--- a/packages/cli/test/cli-program.test.ts
+++ b/packages/cli/test/cli-program.test.ts
@@ -54,6 +54,32 @@ describe('buildKtxProgram', () => {
 
     expect(wrote).toBe('');
   });
+
+  it('adds the Slack community footer to root help', () => {
+    let stdout = '';
+    const io: KtxCliIo = {
+      stdout: {
+        isTTY: false,
+        columns: 80,
+        write: (chunk) => {
+          stdout += chunk;
+        },
+      },
+      stderr: {
+        write: () => undefined,
+      },
+    };
+    const program: Command = buildKtxProgram({
+      io,
+      deps: {},
+      packageInfo: stubPackageInfo(),
+      runInit: async () => 0,
+    });
+
+    program.outputHelp();
+
+    expect(stdout).toContain('Community & support: https://ktx.sh/slack');
+  });
 });
 
 describe('collectCommandFlagsPresent', () => {
diff --git a/packages/cli/test/cli-runtime.test.ts b/packages/cli/test/cli-runtime.test.ts
new file mode 100644
index 00000000..96eb23ff
--- /dev/null
+++ b/packages/cli/test/cli-runtime.test.ts
@@ -0,0 +1,53 @@
+import { describe, expect, it } from 'vitest';
+
+import type { KtxCliIo } from '../src/cli-runtime.js';
+import { writeGlobalExceptionToStderr } from '../src/cli-runtime.js';
+
+function makeIo(stderrIsTty: boolean): { io: KtxCliIo; stderr: () => string } {
+  let stderr = '';
+  const stderrStream = stderrIsTty
+    ? {
+        isTTY: true,
+        columns: 80,
+        on: () => undefined,
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      }
+    : {
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      };
+
+  return {
+    io: {
+      stdout: {
+        write: () => undefined,
+      },
+      stderr: stderrStream,
+    },
+    stderr: () => stderr,
+  };
+}
+
+describe('writeGlobalExceptionToStderr', () => {
+  it('prints the crash Slack hint after a stack on TTY stderr', () => {
+    const testIo = makeIo(true);
+
+    writeGlobalExceptionToStderr(testIo.io, new Error('global boom'));
+
+    expect(testIo.stderr()).toContain('Error: global boom');
+    expect(testIo.stderr()).toContain('This may be a bug');
+    expect(testIo.stderr()).toContain('https://ktx.sh/slack');
+  });
+
+  it('prints crash details without the Slack hint on non-TTY stderr', () => {
+    const testIo = makeIo(false);
+
+    writeGlobalExceptionToStderr(testIo.io, 'global boom');
+
+    expect(testIo.stderr()).toContain('global boom');
+    expect(testIo.stderr()).not.toContain('https://ktx.sh/slack');
+  });
+});
diff --git a/packages/cli/test/community-cta.test.ts b/packages/cli/test/community-cta.test.ts
new file mode 100644
index 00000000..7d21e77e
--- /dev/null
+++ b/packages/cli/test/community-cta.test.ts
@@ -0,0 +1,72 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  SLACK_HELP_FOOTER,
+  SLACK_SETUP_NOTE,
+  writeErrorCommunityHint,
+} from '../src/community-cta.js';
+import type { KtxCliIo } from '../src/cli-runtime.js';
+
+function makeIo(stderrIsTty: boolean): { io: KtxCliIo; stderr: () => string } {
+  let stderr = '';
+  const stderrStream = stderrIsTty
+    ? {
+        isTTY: true,
+        columns: 80,
+        on: () => undefined,
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      }
+    : {
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      };
+
+  return {
+    io: {
+      stdout: {
+        write: () => undefined,
+      },
+      stderr: stderrStream,
+    },
+    stderr: () => stderr,
+  };
+}
+
+describe('community CTA', () => {
+  it('writes the error hint to TTY stderr', () => {
+    const testIo = makeIo(true);
+
+    writeErrorCommunityHint(testIo.io, 'error');
+
+    expect(testIo.stderr()).toContain('Stuck? The ktx community can help');
+    expect(testIo.stderr()).toContain('https://ktx.sh/slack');
+  });
+
+  it('suppresses the error hint for non-TTY stderr', () => {
+    const testIo = makeIo(false);
+
+    writeErrorCommunityHint(testIo.io, 'error');
+
+    expect(testIo.stderr()).toBe('');
+  });
+
+  it('uses stronger crash copy for crash hints', () => {
+    const testIo = makeIo(true);
+
+    writeErrorCommunityHint(testIo.io, 'crash');
+
+    expect(testIo.stderr()).toContain('This may be a bug');
+    expect(testIo.stderr()).toContain('https://ktx.sh/slack');
+  });
+
+  it('exports setup and help copy with the stable Slack URL', () => {
+    expect(SLACK_HELP_FOOTER).toBe('Community & support: https://ktx.sh/slack');
+    expect(SLACK_SETUP_NOTE).toEqual({
+      title: 'Community',
+      body: 'Questions or feedback? Join the ktx Slack: https://ktx.sh/slack',
+    });
+  });
+});
diff --git a/packages/cli/test/io/tty.test.ts b/packages/cli/test/io/tty.test.ts
new file mode 100644
index 00000000..3d5fd2c8
--- /dev/null
+++ b/packages/cli/test/io/tty.test.ts
@@ -0,0 +1,40 @@
+import { describe, expect, it } from 'vitest';
+
+import { isWritableTtyOutput } from '../../src/io/tty.js';
+
+describe('isWritableTtyOutput', () => {
+  it('accepts writable TTY-like output', () => {
+    const output = {
+      isTTY: true,
+      columns: 80,
+      on: () => undefined,
+      write: () => undefined,
+    };
+
+    expect(isWritableTtyOutput(output)).toBe(true);
+  });
+
+  it('rejects non-TTY output', () => {
+    expect(isWritableTtyOutput({ write: () => undefined })).toBe(false);
+  });
+
+  it('rejects output missing stream event support', () => {
+    expect(
+      isWritableTtyOutput({
+        isTTY: true,
+        columns: 80,
+        write: () => undefined,
+      }),
+    ).toBe(false);
+  });
+
+  it('rejects output missing column metadata', () => {
+    const output = {
+      isTTY: true,
+      on: () => undefined,
+      write: () => undefined,
+    };
+
+    expect(isWritableTtyOutput(output)).toBe(false);
+  });
+});
diff --git a/packages/cli/test/setup.test.ts b/packages/cli/test/setup.test.ts
index ecb20520..4d46d08c 100644
--- a/packages/cli/test/setup.test.ts
+++ b/packages/cli/test/setup.test.ts
@@ -652,6 +652,8 @@ describe('setup status', () => {
     expect(testIo.stdout()).toContain('ktx setup');
     expect(testIo.stdout()).not.toContain('ktx agent context --json');
     expect(testIo.stdout()).not.toContain('Optional MCP:');
+    expect(testIo.stdout()).toContain('Community:');
+    expect(testIo.stdout()).toContain('Questions or feedback? Join the ktx Slack: https://ktx.sh/slack');
     expect(testIo.stderr()).toBe('');
   });