memtrace-cochange

name	memtrace-cochange
description	Always use for historical coupling, co-change, what changes with this, hidden dependency, or what else needs to move questions for source code. Do not use git log, git diff, Grep, or manual file search to correlate changes; Memtrace queries co-change and temporal graph data directly.

Overview

Find symbols that historically co-change with a target symbol — ranked by co-occurrence frequency across all episodes. This surfaces behavioral coupling that the static call graph cannot see.

get_impact answers "who calls this?" (structural). get_cochange_context answers "what always moves when this moves?" (historical).

They are complementary. A symbol with no direct callers can still have strong cochange partners if it's always modified alongside another in every commit.

Parameter types: MCP parameters are strictly typed. Numbers (limit, depth, min_size, last_n, etc.) must be JSON numbers — not strings. Use limit: 20, never limit: "20". Passing a string yields MCP error -32602: invalid type: string, expected usize.

Steps

1. Identify the target symbol

Use find_symbol if you need the exact name. The tool matches by name field.

2. Call get_cochange_context

get_cochange_context(
  repo_id: "...",
  symbol: "execute",    // exact symbol name
  limit: 20             // default 20, increase for broader view
)

3. Interpret results

The response contains cochanges[], each with:

• name — symbol name
• kind — Function / Method / Class / Struct
• file_path — where it lives
• cochange_count — how many episodes it shared with the target

High cochange_count = strong historical coupling
→ If you modify the target, you will likely need to touch this too
→ Or it may be the real root cause you should investigate first

4. Cross-reference with call graph

For the top cochange partners, optionally run get_impact to see if the coupling is also structural:

Structural coupling	Historical coupling	Interpretation
Yes	Yes	Core architectural dependency — highest risk
No	Yes	Hidden coupling — only visible through history
Yes	No	Called frequently but changed independently — lower risk

When to Use

• Before modifying a symbol — get blast awareness beyond what get_impact shows
• Incident investigation — when get_impact doesn't explain the blast radius, check cochange history
• Code review — verify that a PR touched all historically-coupled partners
• Refactoring — discover implicit coupling before extracting a module

Common Mistakes

Mistake	Reality
Only using get_impact for blast radius	Structural coupling misses behavioral coupling — always pair with cochange
Ignoring low-in_degree cochange partners	A rarely-called utility with high cochange_count is a strong coupling signal
Using cochange as a dependency map	It's not a dependency graph — it's a change correlation. Two symbols can cochange without any direct relationship.