fix(web): dispose idle MCP server instances to prevent process accumulation

[lytedev]

Issue for this PR

Closes #14091

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Same root cause as #14092 — server.stop() is unreachable dead code after await new Promise(() => {}) in web.ts, and no signal handlers exist. I also added idle eviction of cached Instance entries, which #14092 doesn't cover: without it, each project switch accumulates MCP server processes (~200MB each) for the entire lifetime of the web server, even if those projects are never revisited.

Signal handlers (SIGINT/SIGTERM/SIGHUP) follow the existing worker.ts pattern. Idle eviction sweeps every 60s and disposes instances idle >5 minutes. I didn't touch serve.ts or the SSE cleanup — happy to add those if this gets traction, or #14092 can cover them.

How did you verify your code works?

Ran patched and unpatched instances side by side on the same machine. After switching between 8 projects over ~30 minutes:

• Unpatched: 8 sets of MCP servers accumulated, ~1.65 GB RSS in leaked child processes
• Patched: 0 leaked processes after idle timeout

bun turbo typecheck (16/16 pass), bun turbo test (1172 pass, 0 fail).

Screenshots / recordings

No UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found several related PRs that address similar issues with process management and cleanup:

Potentially Related PRs:

1. fix: resolve memory leaks and zombie processes from missing cleanup handlers #13186 - "fix: resolve memory leaks and zombie processes from missing cleanup handlers"

   • Directly addresses memory leaks and zombie processes from missing cleanup handlers

2. fix(cli): handle SIGHUP to prevent orphaned processes on terminal close #12718 - "fix(cli): handle SIGHUP to prevent orphaned processes on terminal close"

   • Implements signal handlers (SIGHUP) for graceful process cleanup

3. fix(tui): add signal handlers to prevent orphaned processes on terminal close #13848 - "fix(tui): add signal handlers to prevent orphaned processes on terminal close"

   • Similar signal handler approach for TUI mode cleanup

4. fix(opencode): prevent resource leaks in serve/web shutdown and SSE stream cleanup #14092 - "fix(opencode): prevent resource leaks in serve/web shutdown and SSE stream cleanup"

   • Addresses cleanup in web/serve modes, directly related to the web command

5. fix: resolve memory leak issues across multiple subsystems #14650 - "fix: resolve memory leak issues across multiple subsystems"

   • Broader memory leak fixes that may overlap with this PR's scope

These PRs appear to be addressing the same class of issues (process accumulation, memory leaks, signal handlers, and graceful shutdown) across different modes of the application. PR #14092 seems most relevant as it specifically targets web/serve shutdown issues.

[github-actions]

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