feat(cli): improve agent prompts/skills and workspace fork workflow (#9531)

* feat(cli): improve agent prompts/skills and workspace fork workflow

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

* fix(cli): refuse fork --from-branch rename of a base branch

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

* refactor(cli): auto-detect fork branch workflow, drop rt.d.ts refresh and legacy-name warning

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

* docs(skills): reconcile raw-app generate-metadata stance (agent offers+runs)

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

* docs(skills): agent runs all CLI commands, gated on intent not on user typing them

Extends #9467's safe-vs-destructive model: the agent runs consequential commands (sync push, generate-metadata) itself too, gated on explicit user intent rather than handed to the user to type. The explicit-intent rule is the safeguard; an approval prompt is treated as a possible backstop, not assumed (auto-approve/headless runs have none).

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

* Revert "docs(skills): agent runs all CLI commands, gated on intent not on user typing them"

Reverts 9225e1759b. That commit over-reached: #9467 already established the safe-vs-destructive split, and the targeted item-6 fix already removed the passive "tell the user they can run <safe next step>" phrasing. The blanket "agent runs everything" principle pushed deploys to be more eager and carried a wrong "permission layer prompts for approval" claim (untrue in auto-approve/headless mode). Keep deploys conservative.

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

* feat(cli): default fork workspace name/id to the current branch when renaming it

When 'wmill workspace fork' converts the current working branch into the fork branch, default the fork's name and id to that branch (sanitized to a slug, since branch names can contain '/'). Interactive: the prompt is pre-filled (enter to accept); non-interactive (--yes): used automatically. Adds a unit test for the slug derivation.

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

* fix(cli): address fork review — guard fork-branch rename, cap+validate fork id

Two P2s from review:
- --from-branch refused when the current branch is already a fork branch (would detach the existing fork by renaming its branch).
- fork id slug capped to 42 chars (backend max 50 incl. wm-fork- prefix); auto-derived id is slugged; full id validated client-side before existsWorkspace/datatable cloning so an invalid id fails fast instead of leaving cloned Postgres databases behind.

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

---------

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

cli/src/utils/git.ts

@@ -20,6 +20,33 @@ export function getCurrentGitBranch(): string | null {
   }
 }
 
+/** Whether a local branch with this exact name exists. */
+export function gitBranchExists(branchName: string): boolean {
+  const r = spawnSync(
+    "git",
+    ["show-ref", "--verify", "--quiet", `refs/heads/${branchName}`],
+    { stdio: "pipe" },
+  );
+  return r.status === 0;
+}
+
+/**
+ * Rename the currently checked-out branch (`git branch -m <newName>`). Used by
+ * `wmill workspace fork --from-branch` to turn an existing working branch into
+ * the `wm-fork/<base>/<id>` fork branch in place, preserving its commits.
+ */
+export function renameCurrentGitBranch(newName: string): void {
+  const r = spawnSync("git", ["branch", "-m", newName], {
+    encoding: "utf8",
+    stdio: "pipe",
+  });
+  if ((r.status ?? 1) !== 0) {
+    throw new Error(
+      `git branch -m ${newName} failed (exit ${r.status}): ${r.stderr ?? ""}`,
+    );
+  }
+}
+
 export function getOriginalBranchForWorkspaceForks(branchName: string | null): string | null {
   if (!branchName || !branchName.startsWith(WM_FORK_PREFIX)) {
     return null