feat: metric quality improvements and DX enhancements

[bntvllnt]

Summary

Collection of metric quality and developer experience improvements identified during deep analysis testing across 4 repos (self + jarvis-cli 279 files + analytics 12 files + logger 13 files).

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1. Single-file module cohesion scoring (HIGH)

10/12 modules flagged as JUNK_DRAWER by analyze_forces. But 7 of those are single-file modules where cohesion is meaningless (no internal deps possible with 1 file).

community/ (1 file) → cohesion: 0 → JUNK_DRAWER
impact/    (1 file) → cohesion: 0 → JUNK_DRAWER
search/    (1 file) → cohesion: 0 → JUNK_DRAWER
...5 more

Fix: Label single-file modules as LEAF or N/A instead of JUNK_DRAWER.

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2. Tension analysis heuristics for special files (MEDIUM)

analyze_forces recommends splitting:

• types/index.ts — but this is the design-intentional single source of truth for all types
• cli.ts — but this is the entry point orchestrator

Recommendations like "Split into analyzer-index.ts and graph-index.ts" would violate the project architecture.

Fix: Add heuristics to suppress split recommendations for:

• Type hub files (high fan-in, 0 fan-out, all type exports)
• Entry point files (0 fan-in, high fan-out, bin or CLI patterns)

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3. file_context path normalization (MEDIUM)

file_context("src/mcp/index.ts") returns "File not found in graph". Must use "mcp/index.ts" (no src/ prefix). Error message doesn't hint at the correct format.

Fix: Strip common prefixes (src/, lib/, app/) automatically, or include the expected format in the error message.

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4. Git churn integration (LOW)

find_hotspots(metric='churn') always returns 0 for all files. The churn metric exists in the data model but is never populated.

Fix: Integrate git log --numstat to compute per-file change frequency. Churn + complexity = high-value hotspot detection.

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5. Context-aware nextSteps hints (LOW)

nextSteps in tool responses are static regardless of results. For example, find_dead_exports suggests "check if they're truly unused" even when 0 dead exports are found.

Fix: Conditionally generate hints based on result data (empty results, high counts, specific patterns detected).