fix: agent config panel resolves Claude MCP paths from CLAUDE_CONFIG_DIR

[1nderboi]

Summary

• The agent config panel's MCP server list and "From config file (…)" attribution for the claude runtime always read ~/.claude/settings.json + ~/.claude.json, ignoring an agent's own CLAUDE_CONFIG_DIR.
• An agent given its own CLAUDE_CONFIG_DIR (to isolate it from the operator's personal Claude Code config) genuinely spawns isolated — but the panel kept showing the operator's MCP servers, which reads as "the isolation didn't work" and is alarming when the personal config has mail/drive/database connectors.

Fix

• claude::read_config_file now takes an optional config_dir and resolves both settings.json and .claude.json under it when given (matching Claude Code's own CLAUDE_CONFIG_DIR resolution, which relocates both files together) — falling back to ~/.claude/settings.json + ~/.claude.json otherwise.
• reader::mcp_config_file_path_for_runtime resolves the same way for the panel's file-attribution path.
• Both call sites pull CLAUDE_CONFIG_DIR from the agent's own record.env_vars.

Why this scope

The confirmed root cause (and the issue title) is specifically the per-agent CLAUDE_CONFIG_DIR override — the most common way to isolate an agent today. Threading the fully layered effective env (global defaults + persona + per-agent) through would require widening read_config_surface's signature across ~25 call sites for a case the issue doesn't demonstrate a concrete repro for; happy to follow up if that's wanted.

Test plan

• Added unit tests in claude.rs: isolated CLAUDE_CONFIG_DIR reads settings/MCP servers from that dir; an empty isolated dir does not fall back to ~/.claude.json; claude_config_paths nests both files under an explicit dir.
• Added a reader_tests.rs test asserting read_config_surface surfaces MCP extensions and the mcp_config_file_path from the per-agent CLAUDE_CONFIG_DIR, not the default.
• cargo test --manifest-path desktop/src-tauri/Cargo.toml --lib managed_agents::config_bridge — 84 passed, 0 failed.
• cargo clippy --manifest-path desktop/src-tauri/Cargo.toml --all-targets — clean.
• cargo fmt --manifest-path desktop/src-tauri/Cargo.toml --all -- --check — clean.

🤖 Generated with Claude Code