fix(e2b): address review round on cadence config, disposal, and SDK edge cases

- subprocess-e2b: the 20 ms remote poll cadence becomes a validated pollMs
  Config field (each tick is one control-plane request); the README documents
  the latency-versus-request-count trade.
- subprocess-e2b: extract src/remote.ts owning asError, signalOpts,
  commandOpts, delay, waitTick, and one tolerant signalRemoteGroups shared by
  the pgid-keyed process ladder and sid-keyed terminal ladder, so the two
  teardown paths keep identical error tolerance.
- subprocess-e2b: service disposal aggregates sibling cleanup failures into
  one AggregateError instead of discarding all but the first.
- subprocess-e2b: waitForProcessGroupId refuses published group ids <= 1, so
  a same-UID rewrite of the pid file cannot aim termination at kill -- -1;
  README documents the same-UID control-state limitation.
- subprocess-e2b: drain-grace expiry now releases an inherited-output E2B
  callback blocked on host backpressure before disconnecting, so the SDK
  settlement cannot stay pinned behind an unread host stream.
- subprocess-e2b: spawn/spawnTerminal stop validating typed spec fields
  (trust-TypeScript rule; pty-local validates its config before specs exist);
  resolveExecutable rejects separator-containing relative paths per the seam
  contract; terminal setups tracked as a Set of records.
- subprocess-e2b: PTY output push-without-backpressure is a documented
  contract (flowing consumer folds bytes; paused consumer buffers).
- fs-e2b: streamText normalizes the pinned SDK's empty-file '' return into an
  empty stream instead of throwing on getReader().
- e2b overlays: comment the one-world cwd invariant across e2b.cwd,
  workspaceRoot, and bash-local's implicit default workdir.

packages/e2b/subprocess-e2b/tests/terminal.spec.ts

@@ -793,6 +793,8 @@ describe('E2B subprocess terminal service', () => {
   it('rejects invalid executable lookup inputs and results', async () => {
     const { ctx, fake } = await service()
     await expect(ctx.subprocess.resolveExecutable('')).rejects.toThrow('non-empty')
+    await expect(ctx.subprocess.resolveExecutable('./bin/server')).rejects.toThrow('is a relative path')
+    await expect(ctx.subprocess.resolveExecutable('node_modules/.bin/server')).rejects.toThrow('is a relative path')
     await expect(ctx.subprocess.resolveExecutable('node', undefined, AbortSignal.abort(new Error('stop'))))
       .rejects.toThrow('stop')
     fake.resolvedExecutable = 'node\n'
@@ -801,6 +803,15 @@ describe('E2B subprocess terminal service', () => {
     await expect(ctx.subprocess.resolveExecutable('node')).rejects.toThrow('did not resolve')
   })
 
+  it('rejects a non-positive poll cadence at load', async () => {
+    const ctx = new Context()
+    ctx.provide('e2b', runtime(new FakeTerminalSandbox()))
+    await expect(ctx.plugin(E2BSubprocessService, { pollMs: 0 }))
+      .rejects.toThrow('pollMs must be a positive safe integer')
+    const explicit = await ctx.plugin(E2BSubprocessService, { pollMs: 5 })
+    await explicit.dispose()
+  })
+
   it('owns live terminals through service disposal', async () => {
     const { ctx, fiber, fake } = await service()
     const terminal = await ctx.subprocess.spawnTerminal(spec({ signal: new AbortController().signal }))
@@ -873,9 +884,6 @@ describe('E2B subprocess terminal service', () => {
     const { ctx, fiber, fake } = await service()
     for (const request of [
       spec({ argv: [] }),
-      spec({ rows: 0 }),
-      spec({ cols: 1.5 }),
-      spec({ graceMs: 0 }),
       spec({ signal: AbortSignal.abort(new Error('cancelled')) }),
     ]) {
       await expect(ctx.subprocess.spawnTerminal(request)).rejects.toThrow()