feat(server-s3): one Linux user per account (S3) — experimental

Server mode can now run each account as its own Linux user (ah-<name>)
when `agenthub server install-system` has set S3 up. The dashboard
reaches a member only through sudo -u / write-as / pane-launch, reads a
member's files only through owner- and type-checked opens, and hooks
are authenticated by peer uid. Local mode and server mode without S3
are unchanged.

EXPERIMENTAL: tested with fake sudo and fake accounts only. It has not
yet been verified on a real install with real member accounts, sudo or
a real Codex login. Do not offer it to real users yet.

- S3 core: provisioning, per-member tmux servers, the proxy key
  gateway, shared tools in /opt, dropped capabilities for children
  (P0–P5)
- P4: plan and quota per member home
- P6: ~/.claude.json seed; opt-in plugin baseline installed as the
  member; managed-settings spike script (not run)
- P7: Codex account pool (`agenthub accounts add --tool codex`)
- Roles merged with main's admin / analyst / developer: analysts write
  only their own rows, under S3 as well
- Per-account prefs: one implementation (Chat UI + onboarding)
- Security reviews F1–F49 (five rounds), each fix with a regression
  test: symlink/TOCTOU-safe member reads, no host writes in a member
  home, credentials and the data dir never served, owner and folder
  account must agree, pane tokens bound to the pane's uid, bounded
  sudo/tmux/git calls and member reads (no hang or crash from a member),
  async route rejections answer 500 instead of exiting
- Docs: docs/SERVER-MODE.md (S3 model, accepted ceilings, operator
  runbook), docs/plans/server-mode/S3-PLAN.md, CLAUDE.md S3 rules

Tests: server 2838/2841 (3 need 127.0.0.1:3000, held on this box);
client 1162/1162; tsc clean; headers check passes.

Co-Authored-By: Claude <noreply@anthropic.com>

server/lib/ai-tool-jobs.js

@@ -214,6 +214,17 @@ async function finish(j, code) {
     if (code === 0 && j.action === "install" && aiTools.detect(j.tool).installed) {
       aiTools.setEnabled(j.tool, true);
     }
+    // S3: members run the shared copy under /opt/agenthub/tools — refresh it.
+    if (code === 0 && require("./linux-accounts").s3Enabled()) {
+      const shared = require("./shared-tools");
+      const done = j.tool ? [await shared.publish(j.tool)] : await shared.publishAll();
+      for (const r of done) {
+        append(
+          j,
+          `\n[agenthub] ${r.error ? `${r.id}: not shared — ${r.error}` : `shared for every account: ${r.path}`}\n`
+        );
+      }
+    }
   } catch (err) {
     append(j, `\n[agenthub] ${err.message}\n`);
   } finally {