refactor(runtime): collapse speculative portability layers

Remove the one-consumer bounded-read primitive and shared terminal lifecycle controller, make terminal cleanup one awaited provider operation, and reuse one Code Runtime contract suite. Keep only reproduced cancellation and policy fixes; defer unproven replacement, prompt-attribution, and streaming-frame concerns to scoped markers.

packages/fs/fs-local/tests/filesystem.spec.ts

@@ -218,15 +218,6 @@ describe('readText / streamText', () => {
     expect(await fs.readText(await fs.resolve('a.txt'))).toBe('one\ntwo\nthree')
   })
 
-  it('reads complete text through the stable byte bound', async () => {
-    await writeFile(join(dir, 'bounded.txt'), '€abc')
-    const target = await fs.resolve('bounded.txt')
-    expect(await fs.readTextBounded(target, 6)).toBe('€abc')
-    await expect(fs.readTextBounded(target, 5)).rejects.toThrow('exceeds the 5-byte limit')
-    await expect(fs.readTextBounded(target, 0)).rejects.toThrow('positive safe integer')
-    await expect(fs.readTextBounded(target, 6, AbortSignal.abort())).rejects.toMatchObject({ code: 'FS_ABORTED' })
-  })
-
   it('streams the same text', async () => {
     await writeFile(join(dir, 'a.txt'), 'one\ntwo\nthree')
     const target = await fs.resolve('a.txt')

packages/fs/fs-local/tests/fsio.spec.ts

@@ -5,7 +5,7 @@
  * policy and lives in `dsh-fs-policy`, so it is not tested here.
  */
 
-import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import { chmod, mkdtemp, readFile, rename, rm, stat, symlink, unlink, writeFile, mkdir, readdir, realpath } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
@@ -17,7 +17,6 @@ import {
   probeNoFollow,
   readForEdit,
   readWholeText,
-  readWholeTextBounded,
   resolveLocalTarget,
   restoreLineEndings,
   streamWholeText,
@@ -317,66 +316,6 @@ describe('readWholeText', () => {
   })
 })
 
-describe('readWholeTextBounded', () => {
-  it('rejects non-files, binary text, and initial oversize without a full read', async () => {
-    await expect(readWholeTextBounded(localTarget(dir), 10)).rejects.toMatchObject({ code: 'FS_NOT_REGULAR_FILE' })
-    await writeFile(join(dir, 'large'), '12345')
-    await expect(readWholeTextBounded(localTarget(join(dir, 'large')), 4)).rejects.toThrow('exceeds the 4-byte limit')
-    await writeFile(join(dir, 'binary'), Buffer.from([0x61, 0x00, 0x62]))
-    await expect(readWholeTextBounded(localTarget(join(dir, 'binary')), 3)).rejects.toMatchObject({ code: 'FS_NOT_TEXT' })
-  })
-
-  it('detects growth past the bound on the same open handle', async () => {
-    const close = vi.fn(async () => {})
-    const read = vi.fn(async (buffer: Buffer, offset: number, length: number, position: number) => {
-      const bytes = position === 0 ? Buffer.from('abc') : Buffer.from('d')
-      bytes.copy(buffer, offset, 0, Math.min(length, bytes.length))
-      return { bytesRead: Math.min(length, bytes.length), buffer }
-    })
-    vi.resetModules()
-    vi.doMock('node:fs/promises', async (importOriginal) => {
-      const actual = await importOriginal<typeof import('node:fs/promises')>()
-      return {
-        ...actual,
-        open: async () => ({
-          stat: async () => ({ isFile: () => true, size: 3 }),
-          read,
-          close,
-        }),
-      }
-    })
-    try {
-      const isolated = await import('../src/fsio.ts')
-      await expect(isolated.readWholeTextBounded(localTarget('/virtual/growing'), 3))
-        .rejects.toThrow('grew past the 3-byte limit')
-      expect(close).toHaveBeenCalledOnce()
-    } finally {
-      vi.doUnmock('node:fs/promises')
-      vi.resetModules()
-    }
-  })
-
-  it('translates permission and generic open failures', async () => {
-    const failure: { current: Error & { code?: string } } = { current: Object.assign(new Error('denied'), { code: 'EACCES' }) }
-    vi.resetModules()
-    vi.doMock('node:fs/promises', async (importOriginal) => {
-      const actual = await importOriginal<typeof import('node:fs/promises')>()
-      return { ...actual, open: async () => { throw failure.current } }
-    })
-    try {
-      const isolated = await import('../src/fsio.ts')
-      await expect(isolated.readWholeTextBounded(localTarget('/virtual/denied'), 3))
-        .rejects.toMatchObject({ code: 'FS_PERMISSION_DENIED' })
-      failure.current = new Error('open broke')
-      await expect(isolated.readWholeTextBounded(localTarget('/virtual/broken'), 3))
-        .rejects.toMatchObject({ code: 'FS_IO_ERROR' })
-    } finally {
-      vi.doUnmock('node:fs/promises')
-      vi.resetModules()
-    }
-  })
-})
-
 describe('streamWholeText', () => {
   it('streams the whole file as decoded text', async () => {
     const file = join(dir, 'a.txt')