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/lsp/lsp-local/tests/host.spec.ts

@@ -161,6 +161,12 @@ describe('readHostSource', () => {
     await expect(readSource('big.ts', 10)).rejects.toThrow(/10-byte limit/)
   })
 
+  it('counts the complete UTF-8 byte length at the configured boundary', async () => {
+    await writeFile(join(ws, 'multibyte.ts'), '€abc')
+    await expect(readSource('multibyte.ts', 6)).resolves.toMatchObject({ text: '€abc' })
+    await expect(readSource('multibyte.ts', 5)).rejects.toThrow(/5-byte limit/)
+  })
+
   it('rejects a non-UTF-8 source', async () => {
     await writeFile(join(ws, 'bin.ts'), Buffer.from([0xff, 0xfe, 0x00]))
     await expect(readSource('bin.ts')).rejects.toThrow(/invalid UTF-8|binary file/)

packages/lsp/lsp-local/tests/lifecycle.spec.ts

@@ -328,14 +328,17 @@ describe('lsp-local end to end over a fake server', () => {
     await expect(disposing).resolves.toBeUndefined()
   })
 
-  it('aborts a queued source read when the provider is disposed', async () => {
+  it('aborts a queued source stream when the provider is disposed', async () => {
     const ctx = await mount({ LSP_FAKE_DEF: 'null' })
     const fs = ctx.fs
     const started = Promise.withResolvers<AbortSignal>()
-    vi.spyOn(fs, 'readTextBounded').mockImplementation(async (_target, _maxBytes, signal) => {
+    vi.spyOn(fs, 'streamText').mockImplementation(async (_target, signal) => {
       if (signal === undefined) throw new Error('source read missing provider lifetime signal')
       started.resolve(signal)
-      return await rejectWhenAborted(signal)
+      return (async function* () {
+        await rejectWhenAborted(signal)
+        yield ''
+      })()
     })
 
     const pending = ctx.lsp.query(query('goToDefinition'))