feat(ssh): wave 2 — route filesystem/shell tools behind ExecBackend

Wave 2 of transparent SSH support (4 parallel owner-agents on disjoint
tool packages). The tools now resolve an ExecBackend per-call from
ctx.computerId and call backend.spawn / backend.readFile / etc. instead of
node:fs and node:child_process directly — so they are transport-agnostic
(local now; remote over SSH later, transparent to the agent). Still LOCAL-ONLY
this wave (computerId always undefined -> LocalExecBackend, behavior-identical).

- tool-shell: factory takes resolveBackend; execute calls backend.spawn.
  spawn.ts DELETED (realSpawn was a verbatim duplicate of exec-backend's
  LocalExecBackend.spawn — logic moved to the sanctioned shared package).
  manifest dependsOn:[exec-backend]; host.getService at activation.
- tool-read-file: readFile/stat/readdir -> backend.* (pure logic untouched;
  ENOENT .code branches kept).
- tool-write-file: exists/stat/writeFile -> backend.* (pure logic untouched).
- tool-edit-file: readFile/writeFile -> backend.* + forward-compatible REMOTE
  diagnostics skip (ctx.computerId set -> skip LSP, return empty — plan §6.1;
  local path byte-identical to today). LSP lookup stays lazy.
- orchestrator: pre-wired @dispatch/exec-backend dep into the 4 tool
  package.jsons + bun install (build/config, my lane) so isolated verify
  resolved cleanly; agents added the ../exec-backend tsconfig ref.

Verified: tsc -b EXIT 0, biome clean, 1599 vitest pass (was 1592).
Refs: notes/ssh-support-plan.md (decisions §0.5/§13). No merge or push.

1 files changed, 0 insertions, 87 deletions

diff --git a/packages/tool-shell/src/spawn.ts b/packages/tool-shell/src/spawn.ts
deleted file mode 100644
index 9b1d7e4..0000000
--- a/packages/tool-shell/src/spawn.ts
+++ /dev/null
@@ -1,87 +0,0 @@
-import { spawn as nodeSpawn } from "node:child_process";
-import type { SpawnResult, SpawnShell } from "./shell.js";
-
-export const realSpawn: SpawnShell = (params): Promise<SpawnResult> => {
-	return new Promise<SpawnResult>((resolve) => {
-		// detached: true puts the child in its own process group (pgid = child.pid).
-		// This lets us kill the entire group (child + any grandchildren that inherit
-		// the pipes) via process.kill(-pgid, "SIGKILL") on abort/timeout, so a
-		// backgrounded grandchild can't keep the stdio pipes open and stall the
-		// promise on child.on("close").
-		const child = nodeSpawn("sh", ["-c", params.command], {
-			cwd: params.cwd,
-			stdio: ["ignore", "pipe", "pipe"],
-			detached: true,
-		});
-
-		let settled = false;
-		let timedOut = false;
-		let timer: ReturnType<typeof setTimeout> | undefined;
-
-		/** Kill the entire child process group (best-effort — group may be gone). */
-		const killGroup = () => {
-			if (child.pid !== undefined) {
-				try {
-					process.kill(-child.pid, "SIGKILL");
-				} catch {
-					// Process group may already be gone — ignore.
-				}
-			}
-		};
-
-		/** Remove the abort listener and clear the timeout timer (no leaks). */
-		const cleanup = () => {
-			if (timer !== undefined) {
-				clearTimeout(timer);
-				timer = undefined;
-			}
-			params.signal.removeEventListener("abort", onAbort);
-		};
-
-		/** Resolve once, then clean up so listeners/timers never leak. */
-		const settle = (result: SpawnResult) => {
-			if (settled) return;
-			settled = true;
-			cleanup();
-			resolve(result);
-		};
-
-		const onAbort = () => {
-			if (settled) return;
-			killGroup();
-			// Resolve immediately — do NOT wait for child.on("close"), which may
-			// never fire if a grandchild holds the pipes open.
-			settle({ exitCode: null, timedOut: false, aborted: true });
-		};
-		params.signal.addEventListener("abort", onAbort, { once: true });
-
-		timer = setTimeout(() => {
-			if (settled) return;
-			timedOut = true;
-			killGroup();
-			// Resolve immediately — same reasoning as abort.
-			settle({ exitCode: null, timedOut: true, aborted: false });
-		}, params.timeout);
-
-		child.stdout.on("data", (chunk: Buffer) => {
-			params.onOutput(chunk.toString(), "stdout");
-		});
-
-		child.stderr.on("data", (chunk: Buffer) => {
-			params.onOutput(chunk.toString(), "stderr");
-		});
-
-		// Normal-completion path: wait for "close" so all stdout/stderr is captured.
-		// If abort/timeout already settled, this is a no-op (settled === true).
-		child.on("close", (code) => {
-			settle({ exitCode: code, timedOut, aborted: false });
-		});
-
-		// Spawn error (e.g. bad cwd, sh not found). Kill the group just in case
-		// and resolve — never leave the promise pending.
-		child.on("error", () => {
-			killGroup();
-			settle({ exitCode: 1, timedOut: false, aborted: false });
-		});
-	});
-};