feat(cli): show migration warning on all project-reaching commands

Follow-up to the previous commit, which narrowed the warning to exclude
worktree commands. That call was driven by a non-hermetic e2e test (it read
the dev machine's real ~/.webmux registry), not by merit — so revert the
narrowing: the nudge now fires on every command that reaches a project
(oneshot/linear/project + worktree commands), still excluding `project
migrate`. It's silent unless other servers exist, transient until you
consolidate, and on stderr.

Make the webmux.test.ts e2e spawns hermetic by isolating HOME, so the
registry read sees an empty dir regardless of what's running locally.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hugocasa

bin/src/webmux.test.ts

@@ -174,10 +174,16 @@ describe("webmux entrypoint", () => {
     const nestedDir = join(repoRoot, "nested", "dir");
     await mkdir(nestedDir, { recursive: true });
 
+    // Isolate HOME so the migration-warning's registry read (~/.webmux/instances)
+    // sees an empty dir, not the dev machine's real running instances.
+    const home = await mkdtemp(join(tmpdir(), "webmux-home-"));
+    tempDirs.push(home);
+
     const result = Bun.spawnSync(["bun", webmuxEntry, "open", "missing-branch"], {
       cwd: nestedDir,
       stdout: "pipe",
       stderr: "pipe",
+      env: { ...process.env, HOME: home },
     });
     const stderr = decoder.decode(result.stderr).trim();
 
@@ -211,12 +217,18 @@ describe("webmux entrypoint", () => {
     const worktreePath = join(worktreesRoot, "feature-self-remove");
     runOrThrow(["git", "worktree", "add", "-b", "feature-self-remove", worktreePath], repoRoot);
 
+    // Isolate HOME so the migration-warning's registry read sees an empty dir,
+    // keeping stderr clean regardless of what's running on the dev machine.
+    const home = await mkdtemp(join(tmpdir(), "webmux-home-"));
+    tempDirs.push(home);
+
     const result = Bun.spawnSync(["bun", webmuxEntry, "remove", "feature-self-remove"], {
       cwd: worktreePath,
       stdout: "pipe",
       stderr: "pipe",
       env: {
         ...process.env,
+        HOME: home,
         PATH: `${fakeBin}:${process.env.PATH ?? ""}`,
       },
     });

bin/src/webmux.ts

@@ -353,17 +353,17 @@ async function main(args: string[] = process.argv.slice(2)): Promise<void> {
     }
   }
 
-  // Nudge toward consolidation when other webmux servers are running — on the
-  // occasional management commands (oneshot/linear/project), but NOT the
-  // high-frequency worktree commands (list/open/send/…) where a per-invocation
-  // warning would be noisy, nor `project migrate` (which consolidates them
-  // itself). Cheap: a local registry read, silent unless peers exist, and to
-  // stderr so it never pollutes piped output.
+  // Nudge toward consolidation when other webmux servers are running, on any
+  // command that reaches a project (everything dispatched below) except
+  // `project migrate`, which consolidates them itself. Cheap: a local registry
+  // read, silent unless peers exist, and to stderr so it never pollutes piped
+  // output. Only relevant before the user has consolidated, so it's transient.
   const isProjectMigrate = parsed.command === "project" && parsed.commandArgs[0] === "migrate";
-  const isOccasionalServerCommand = parsed.command === "oneshot"
+  const reachesAProject = parsed.command === "oneshot"
     || parsed.command === "linear"
-    || parsed.command === "project";
-  if (isOccasionalServerCommand && !isProjectMigrate) {
+    || parsed.command === "project"
+    || isWorktreeCommand(parsed.command);
+  if (reachesAProject && !isProjectMigrate) {
     const { warnIfOtherInstances } = await import("./migrate.ts");
     warnIfOtherInstances(effectivePort);
   }