refactor(audit): reduce complexity of analyze_all in mcp.rs

[github-actions]

What was complex

analyze_all in src/audit/analyzers/mcp.rs had a cognitive complexity of 19 (threshold: 15). The function combined:

• Directory validation with a 3-arm match
• A nested double for loop (files → lines)
• JSON parsing and event dispatch via a 4-arm match (tool_call / tool_error / server_error / server_start|stop), each with several if guards
• Two post-loop phases building tool summaries and server health rollups (3 more loops + inline ternary for error_rate)

All of this lived in one ~200-line function with up to 5 levels of nesting.

What changed

Introduced EventAccumulators — a struct that owns the accumulation state (per_tool, observed_servers, server_error_counts, failures, saw_recognizable_event) and exposes four focused methods:

Method	Responsibility
on_tool_call(&Value)	Register a tool call in per-tool stats and observed servers
on_tool_error(Value)	Register a tool error, update stats, record failure report
on_server_error(Value)	Update server error counts, record failure report
on_server_lifecycle(&Value)	Register server start/stop in observed servers
process_event(&str, Value)	One-line dispatch to the above four methods

Extracted four free functions:

• ensure_mcpg_logs_dir_exists — directory validation (3-arm match with early-return semantics)
• process_log_files — file reading + line dispatch loop
• build_tool_summaries — constructs and sorts Vec<MCPToolSummary> from accumulated state
• build_server_health_list — builds server rollups from three accumulation maps and computes error_rate/unreliable

analyze_all is now a 6-line orchestrator with zero nesting of its own.

Before / After

Metric	Before	After
analyze_all cognitive complexity	19	< 15 (zero Clippy warnings at threshold=15)
Lines in analyze_all	~200	~16
Max nesting depth	5	1

Verification

• cargo build — clean
• cargo test — all tests pass (including the MCP analyzer unit tests in the same file)
• cargo clippy --all-targets --all-features — clean
• cargo clippy ... -W clippy::cognitive_complexity with threshold=15 — zero findings for src/audit/analyzers/mcp.rs

Warning

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