refactor(host-kit): one narrow capability port per export

The four technical barrels (exec/fs/values/request) grouped by category
rather than by capability, so a consumer needing one mechanic evaluated
unrelated ones. Each export is now a single capability over the host
machine: command, process, diagnostics, retry, archive, file, request,
version. A port re-exports only what a consumer of that capability uses,
and every port carries its own eager-closure row.

Most of the old values barrel was never host mechanics. Pure record
readers, config-source values, result text, memoization, async scoping,
coordinate validation, and device-scope parsing touch no process, file, or
environment, so they join kernel's other primitives instead.

Closures fall accordingly: capture-kit's png-worker-client from 20 to 10,
png-resize from 28 to 18, session-teardown from 79 to 68, and the CLI from
386 to 380.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018VngeKZH6zBuJzNBk5YzUH

Author: claude

docs/adr/0019-request-bound-platform-runtime.md

@@ -137,11 +137,18 @@ selection, R11/R13 package enumeration, and the composite typecheck project list
 > exports maps) forces every shared file onto a declared domain owner, and the paragraph above
 > is amended to name that layout rather than let capture-kit absorb it:
 >
-> - `@agent-device/host-kit` owns generic host mechanics — process execution, supervision, and
->   diagnostics; archives, streams, atomic files, locks, and path/device isolation; small host
->   value helpers; request-scoped plumbing — behind a small deep surface of exactly four seams:
->   `exec`, `fs`, `values`, `request`. Modules under `src/internal/` are reachable only through
->   those seams; consumers import a seam, never an internal module.
+> - `@agent-device/host-kit` owns mechanics that act on the host machine, and nothing else. Each
+>   export is one narrow capability port, not a category barrel: `command` (running host
+>   commands), `process` (observing and owning host processes), `diagnostics`, `retry`
+>   (deadline/backoff/sleep), `archive` (bounded extraction and byte limits), `file` (atomic
+>   publishes, locks, path resolution), `request` (request-scoped cancellation and progress),
+>   and `version` (the installed version off disk). Modules under `src/internal/` are reachable
+>   only through a port, and a port may only hold mechanics a consumer of that capability
+>   needs — the eager-closure row per port is what keeps that honest.
+> - A helper that touches no process, file, or environment is not host mechanics and does not
+>   belong here: pure record readers, config-source values, result text, memoization, async
+>   scoping, coordinate validation, and device-scope parsing live in `@agent-device/kernel`
+>   beside its other primitives.
 > - `@agent-device/capture-kit` owns capture, snapshot, and recording behavior — PNG tooling,
 >   screenshot density and pixel diffing, snapshot occlusion, mobile snapshot semantics,
 >   quality verdicts and backend capability tables. Snapshot *behavior* is capture domain, not

packages/capture-kit/src/png-worker-client.ts

@@ -1,5 +1,5 @@
 import { Worker } from 'node:worker_threads';
-import { emitDiagnostic } from '@agent-device/host-kit/exec';
+import { emitDiagnostic } from '@agent-device/host-kit/diagnostics';
 import { AppError, toAppErrorCode } from '@agent-device/kernel/errors';
 import { resolveInternalEntryModulePath } from './internal-entry.ts';
 import { decodePng, PNG } from './png.ts';

packages/host-kit/package.json

@@ -3,7 +3,7 @@
   "version": "0.0.0",
   "private": true,
   "type": "module",
-  "description": "Private generic host mechanics behind four deep seams: process execution and supervision (exec), filesystem and archive guards (fs), pure value helpers (values), and request-scoped plumbing (request). Internal workspace package bundled into the published agent-device artifact.",
+  "description": "Private host-mechanics package: each export is one narrow capability port over the host machine \u2014 running commands, observing and owning processes, diagnostics, retry/deadline, archive extraction, durable files and locks, request-scoped plumbing, and the installed version.",
   "dependencies": {
     "@agent-device/contracts": "workspace:*",
     "@agent-device/kernel": "workspace:*",
@@ -15,21 +15,37 @@
     "@types/yauzl": "^3.4.0"
   },
   "exports": {
-    "./exec": {
-      "types": "./src/exec.ts",
-      "default": "./src/exec.ts"
+    "./archive": {
+      "types": "./src/archive.ts",
+      "default": "./src/archive.ts"
     },
-    "./fs": {
-      "types": "./src/fs.ts",
-      "default": "./src/fs.ts"
+    "./command": {
+      "types": "./src/command.ts",
+      "default": "./src/command.ts"
+    },
+    "./diagnostics": {
+      "types": "./src/diagnostics.ts",
+      "default": "./src/diagnostics.ts"
+    },
+    "./file": {
+      "types": "./src/file.ts",
+      "default": "./src/file.ts"
+    },
+    "./process": {
+      "types": "./src/process.ts",
+      "default": "./src/process.ts"
     },
     "./request": {
       "types": "./src/request.ts",
       "default": "./src/request.ts"
     },
-    "./values": {
-      "types": "./src/values.ts",
-      "default": "./src/values.ts"
+    "./retry": {
+      "types": "./src/retry.ts",
+      "default": "./src/retry.ts"
+    },
+    "./version": {
+      "types": "./src/version.ts",
+      "default": "./src/version.ts"
     }
   }
 }

packages/host-kit/src/archive.ts

@@ -0,0 +1,4 @@
+export { archiveTypeFromPath, extractArchiveSafely } from './internal/archive-extraction.ts';
+export { ArchiveBudget, type ArchiveManifestEntry } from './internal/archive-safety.ts';
+export { MAX_ARTIFACT_COMPRESSED_BYTES } from './internal/artifact-limits.ts';
+export { createByteLimitStream } from './internal/byte-limit-stream.ts';

packages/host-kit/src/command.ts

@@ -0,0 +1,24 @@
+export {
+  coerceExecResult,
+  type CommandExecutorOverride,
+  type ExecBackgroundOptions,
+  type ExecBackgroundResult,
+  type ExecDetachedExit,
+  execFailureDetails,
+  type ExecOptions,
+  type ExecResult,
+  isExecutablePath,
+  requireExecSuccess,
+  resolveExecutableOverridePath,
+  resolveFileOverridePath,
+  runCmd,
+  runCmdBackground,
+  runCmdDetached,
+  runCmdDetachedMonitored,
+  runCmdStreaming,
+  runCmdSync,
+  whichCmd,
+  withCommandExecutorOverride,
+  withoutCommandExecutorOverride,
+} from './internal/exec.ts';
+export { shellQuote, shellQuoteIfNeeded } from './internal/shell-quote.ts';

packages/host-kit/src/diagnostics.ts

@@ -0,0 +1,11 @@
+export {
+  countDiagnosticEventsByPhase,
+  createRequestId,
+  emitDiagnostic,
+  flushDiagnosticsToSessionFile,
+  getDiagnosticsMeta,
+  registerDiagnosticSensitiveValue,
+  updateDiagnosticsScope,
+  withDiagnosticsScope,
+  withDiagnosticTimer,
+} from './internal/diagnostics.ts';

packages/host-kit/src/exec.ts

@@ -0,0 +1,7 @@
+export {
+  isAtomicPublishTemporaryPath,
+  publishFileSync,
+  withAtomicPublishTempPathSync,
+} from './internal/atomic-file.ts';
+export { expandUserHomePath, resolveUserPath } from './internal/path-resolution.ts';
+export { acquireProcessLock, type ProcessLockOwner } from './internal/process-lock.ts';