diff --git a/.agents/command/.npmignore b/.agents/command/.npmignore
new file mode 100644
index 000000000..6524d100e
--- /dev/null
+++ b/.agents/command/.npmignore
@@ -0,0 +1,10 @@
+# Internal-only assets — never ship to npm registry.
+# See script/package-layout-exclusion.test.ts for the enforcing guard.
+# Root .npmignore does not work for directories listed in package.json#files
+# under Bun 1.3.x, so the guard lives co-located with the published content.
+__*/
+__*.md
+.private/
+.draft/
+.private.md
+.draft.md
diff --git a/.agents/skills/.npmignore b/.agents/skills/.npmignore
new file mode 100644
index 000000000..6524d100e
--- /dev/null
+++ b/.agents/skills/.npmignore
@@ -0,0 +1,10 @@
+# Internal-only assets — never ship to npm registry.
+# See script/package-layout-exclusion.test.ts for the enforcing guard.
+# Root .npmignore does not work for directories listed in package.json#files
+# under Bun 1.3.x, so the guard lives co-located with the published content.
+__*/
+__*.md
+.private/
+.draft/
+.private.md
+.draft.md
diff --git a/.opencode/command/.npmignore b/.opencode/command/.npmignore
new file mode 100644
index 000000000..6524d100e
--- /dev/null
+++ b/.opencode/command/.npmignore
@@ -0,0 +1,10 @@
+# Internal-only assets — never ship to npm registry.
+# See script/package-layout-exclusion.test.ts for the enforcing guard.
+# Root .npmignore does not work for directories listed in package.json#files
+# under Bun 1.3.x, so the guard lives co-located with the published content.
+__*/
+__*.md
+.private/
+.draft/
+.private.md
+.draft.md
diff --git a/.opencode/skills/.npmignore b/.opencode/skills/.npmignore
new file mode 100644
index 000000000..6524d100e
--- /dev/null
+++ b/.opencode/skills/.npmignore
@@ -0,0 +1,10 @@
+# Internal-only assets — never ship to npm registry.
+# See script/package-layout-exclusion.test.ts for the enforcing guard.
+# Root .npmignore does not work for directories listed in package.json#files
+# under Bun 1.3.x, so the guard lives co-located with the published content.
+__*/
+__*.md
+.private/
+.draft/
+.private.md
+.draft.md
diff --git a/script/package-layout-exclusion.test.ts b/script/package-layout-exclusion.test.ts
new file mode 100644
index 000000000..1fb0e37d3
--- /dev/null
+++ b/script/package-layout-exclusion.test.ts
@@ -0,0 +1,208 @@
+/// <reference types="bun-types" />
+
+import { afterAll, beforeAll, describe, expect, test } from "bun:test"
+import { existsSync, mkdirSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs"
+import { dirname, join, relative, sep } from "node:path"
+import { fileURLToPath } from "node:url"
+
+const repositoryRoot = fileURLToPath(new URL("..", import.meta.url))
+const packageJsonPath = join(repositoryRoot, "package.json")
+const fakeArtifactName = "__internal-fake-do-not-ship-test-artifact"
+const packageAssetRoots = [".opencode/command", ".opencode/skills", ".agents/command", ".agents/skills"] as const
+const fakeInternalSkillArtifactRootPaths = [
+  `.opencode/skills/${fakeArtifactName}`,
+  `.agents/skills/${fakeArtifactName}`,
+] as const
+const fakeInternalSkillArtifactPaths = [
+  `${fakeInternalSkillArtifactRootPaths[0]}/SKILL.md`,
+  `${fakeInternalSkillArtifactRootPaths[1]}/SKILL.md`,
+] as const
+const fakeInternalCommandArtifactPaths = [
+  `.opencode/command/${fakeArtifactName}.md`,
+  `.agents/command/${fakeArtifactName}.md`,
+] as const
+const fakeInternalArtifactCleanupPaths = [
+  ...fakeInternalSkillArtifactRootPaths,
+  ...fakeInternalCommandArtifactPaths,
+] as const
+
+let originalPackageJsonText: string | null = null
+let packageJsonWasTemporarilyModified = false
+
+class PackDryRunError extends Error {
+  constructor(readonly exitCode: number, readonly stderr: string) {
+    super(`bun pm pack --dry-run failed with exit code ${exitCode}: ${stderr}`)
+    this.name = "PackDryRunError"
+  }
+}
+
+class PackageFilesAnchorError extends Error {
+  constructor() {
+    super("package.json files list no longer contains the postinstall.mjs anchor")
+    this.name = "PackageFilesAnchorError"
+  }
+}
+
+function toPackagePath(filePath: string): string {
+  return relative(repositoryRoot, filePath).split(sep).join("/")
+}
+
+function collectPackagePathsRecursively(rootPath: string): string[] {
+  const collectedPaths: string[] = []
+  const directories = [rootPath]
+
+  while (directories.length > 0) {
+    const currentDirectory = directories.pop()
+    if (!currentDirectory) {
+      continue
+    }
+
+    for (const entry of readdirSync(currentDirectory, { withFileTypes: true })) {
+      const entryPath = join(currentDirectory, entry.name)
+      if (entry.isDirectory()) {
+        directories.push(entryPath)
+        continue
+      }
+
+      if (entry.isFile()) {
+        collectedPaths.push(toPackagePath(entryPath))
+      }
+    }
+  }
+
+  return collectedPaths
+}
+
+function parsePackedPaths(output: string): Set<string> {
+  const packedPaths = new Set<string>()
+  const packedPathPattern = /^packed\s+\S+\s+(.+)$/
+
+  for (const line of output.split("\n")) {
+    const match = packedPathPattern.exec(line)
+    const packedPath = match?.at(1)
+    if (packedPath) {
+      packedPaths.add(packedPath)
+    }
+  }
+
+  return packedPaths
+}
+
+async function packDryRunPaths(): Promise<Set<string>> {
+  const packProcess = Bun.spawn({
+    cmd: ["bun", "pm", "pack", "--dry-run"],
+    cwd: repositoryRoot,
+    stdout: "pipe",
+    stderr: "pipe",
+  })
+  const [stdout, stderr, exitCode] = await Promise.all([
+    new Response(packProcess.stdout).text(),
+    new Response(packProcess.stderr).text(),
+    packProcess.exited,
+  ])
+
+  if (exitCode !== 0) {
+    throw new PackDryRunError(exitCode, stderr)
+  }
+
+  return parsePackedPaths(stdout)
+}
+
+function withPackageAssetRoots(packageJsonText: string): string {
+  const missingAssetRoots = packageAssetRoots.filter((rootPath) => !packageJsonText.includes(`"${rootPath}"`))
+  if (missingAssetRoots.length === 0) {
+    return packageJsonText
+  }
+
+  const filesAnchor = '    "postinstall.mjs",\n'
+  if (!packageJsonText.includes(filesAnchor)) {
+    throw new PackageFilesAnchorError()
+  }
+
+  const insertedAssetRoots = missingAssetRoots.map((rootPath) => `    "${rootPath}",`).join("\n")
+  return packageJsonText.replace(filesAnchor, `${filesAnchor}${insertedAssetRoots}\n`)
+}
+
+function preparePackageJsonForDotAssetPacking(): void {
+  const packageJsonText = readFileSync(packageJsonPath, "utf8")
+  originalPackageJsonText = packageJsonText
+  const packageJsonTextWithAssetRoots = withPackageAssetRoots(packageJsonText)
+  packageJsonWasTemporarilyModified = packageJsonTextWithAssetRoots !== packageJsonText
+
+  if (packageJsonWasTemporarilyModified) {
+    writeFileSync(packageJsonPath, packageJsonTextWithAssetRoots)
+  }
+}
+
+function restorePackageJson(): void {
+  if (packageJsonWasTemporarilyModified && originalPackageJsonText !== null) {
+    writeFileSync(packageJsonPath, originalPackageJsonText)
+  }
+}
+
+function removeFakeInternalArtifacts(): void {
+  for (const packagePath of fakeInternalArtifactCleanupPaths) {
+    rmSync(join(repositoryRoot, packagePath), { recursive: true, force: true })
+  }
+}
+
+function writeFakeInternalArtifacts(packagePaths: readonly string[]): void {
+  for (const packagePath of packagePaths) {
+    const artifactPath = join(repositoryRoot, packagePath)
+    mkdirSync(dirname(artifactPath), { recursive: true })
+    writeFileSync(artifactPath, "# Fake internal artifact for package-layout-exclusion.test.ts\n")
+  }
+}
+
+function collectExistingFakeInternalSkillArtifactPaths(): string[] {
+  return fakeInternalSkillArtifactRootPaths
+    .filter((packagePath) => existsSync(join(repositoryRoot, packagePath)))
+    .flatMap((packagePath) => collectPackagePathsRecursively(join(repositoryRoot, packagePath)))
+    .sort()
+}
+
+describe("published package layout exclusions", () => {
+  beforeAll(() => {
+    removeFakeInternalArtifacts()
+
+    try {
+      preparePackageJsonForDotAssetPacking()
+      writeFakeInternalArtifacts([...fakeInternalSkillArtifactPaths, ...fakeInternalCommandArtifactPaths])
+    } catch (error) {
+      removeFakeInternalArtifacts()
+      restorePackageJson()
+      throw error
+    }
+  })
+
+  afterAll(() => {
+    removeFakeInternalArtifacts()
+    restorePackageJson()
+  })
+
+  test("#given internal-only skill assets #when packing package #then forbidden skill assets do not ship", async () => {
+    // given
+    expect(collectExistingFakeInternalSkillArtifactPaths()).toEqual(fakeInternalSkillArtifactPaths.toSorted())
+
+    // when
+    const packedPaths = await packDryRunPaths()
+
+    // then
+    const packedInternalSkillPaths = fakeInternalSkillArtifactPaths.filter((packagePath) => packedPaths.has(packagePath))
+    expect(packedInternalSkillPaths).toEqual([])
+  })
+
+  test("#given internal-only command assets #when packing package #then forbidden command assets do not ship", async () => {
+    // given
+    for (const packagePath of fakeInternalCommandArtifactPaths) {
+      expect(existsSync(join(repositoryRoot, packagePath))).toBe(true)
+    }
+
+    // when
+    const packedPaths = await packDryRunPaths()
+
+    // then
+    const packedInternalCommandPaths = fakeInternalCommandArtifactPaths.filter((packagePath) => packedPaths.has(packagePath))
+    expect(packedInternalCommandPaths).toEqual([])
+  })
+})