feat(web): restart the agent session from cmd+k to load new skills and plugins

[t3dotgg]

After adding skills, plugins, or MCP servers, there was no way to make a thread pick them up. The agent process kept its old setup, and the composer's / and $ menus scanned each folder only once, so new skills never showed until the server restarted.

Now Restart agent session in cmd+k stops the thread's provider process. The conversation stays: the next message starts a fresh process that resumes it and loads the new setup. The action also asks the server to scan the thread's folder again (new fresh flag on server.refreshProviders), so the menus update right away.

• A fresh scan also clears the instance's discovery caches, so Claude plugin commands update.
• Other providers' cached menus for the same folder are dropped and fill again when next used.
• Antigravity keeps the rescanned skills when its session events republish.
• Stop and refresh failures show the palette's error toast.

Reviewed with sol-loop: 3 rounds with GPT-6.1 Sol on default effort.

🤖 Generated with Claude Code (Claude Opus 5.5)

Closes #11497

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ The exact PR base did not have a successful artifact. Baseline uses the latest successful main measurement shown below.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	−2 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.1 KiB	+19 B (+0.3%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−21 B (−0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.3 KiB	56.2 KiB	−44 B (−0.1%)	66.4 KiB	✅
Codex	Live turn messages	10	9	−1 (−10.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−8 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+5 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−13 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 408ff8a · PR result: db5e0bd · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.0 KiB
• Claude decoded thread snapshot: 114.7 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This adds a new command-palette workflow that stops the current agent session and refreshes provider, plugin, skill, MCP, and workspace state across several runtime layers. The opt-in flag preserves existing callers, but the cross-layer workflow and session lifecycle side effect make the change non-trivial.

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