fix(mcp): dispatch plugin drivers via the registry + harden the --mcp subprocess

[ymadd]

Summary

MCP could only reach built-in mysql/postgres/sqlite connections — every plugin-driven connection (Hacker News, Redis, …) failed with Unsupported driver. This routes all MCP driver operations through the shared driver registry (the same path the GUI uses) and registers the built-in + installed plugin drivers when the standalone --mcp subprocess starts.

Closes #255.

What changed

• Registry dispatch: schema resource, list_tables, describe_table, run_query, and pre-flight EXPLAIN now resolve the driver via registry::get_driver instead of a hardcoded match.
• Subprocess driver registration: --mcp mode registers the three built-ins + installed plugins (load_plugins_with_configs), honoring active_external_drivers.

Hardening surfaced by reaching plugins from MCP

• Bound plugin RPC calls with a timeout (120 s call / 15 s initialize) so a wedged plugin can't block the single-threaded request loop forever, and cancel the pending entry on timeout so it doesn't leak.
• kill_on_drop the plugin child so it isn't orphaned when the subprocess exits on stdin EOF.
• Refuse plugins that claim a built-in driver id (mysql/postgres/sqlite).
• Resolve resources/read through the keychain/SSH-aware path.
• Initialize the logger in --mcp mode (stderr only) so plugin-load errors are visible.
• Stop cleanly instead of panicking when a stdout write fails (BrokenPipe).
• Run describe_table's column/FK/index fetches concurrently.

Test plan

• cargo build clean (no warnings) on latest main
• cargo test --lib plugins passes
• Verified end-to-end against a Hacker News plugin connection via the --mcp binary: list_tables → ["stories"], run_query → real rows, resources/read → schema (previously all Unsupported driver)
• Confirmed no orphaned plugin process remains after the --mcp subprocess exits

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (5 files)

• src-tauri/src/lib.rs — Initialize logger in --mcp mode before starting the MCP server
• src-tauri/src/mcp/mod.rs — Registry dispatch for all MCP driver operations; adds register_drivers_for_mcp and resolve_db_driver; refactors handle_read_resource, tool_list_tables, tool_describe_table, and tool_run_query to use the shared driver registry instead of hardcoded match arms; runs metadata fetches concurrently in describe_table; handles BrokenPipe gracefully on stdout writes
• src-tauri/src/mcp/preflight.rs — Uses driver_registry::get_driver for EXPLAIN dispatch instead of hardcoded driver match
• src-tauri/src/plugins/driver.rs — Adds PluginCommand enum with Call/Cancel; introduces call_with_timeout with 120s call / 15s init ceilings; sends Cancel on timeout to prevent orphaned pending entries; adds kill_on_drop(true) to prevent orphaned plugin processes on subprocess exit
• src-tauri/src/plugins/manager.rs — Extracts load_plugins_with_configs for non-Tauri MCP use; adds collision guard to refuse plugins claiming built-in driver IDs

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_{Reviewed by kimi-k2.6 · 435,773 tokens}

[debba]

Good catch! I will check it ASAP