FAFO™ Engineering Evidence
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P-004 · Blast Radius

Sub-second graph trace, before code is written.

Live Reproducible Measured

Before any code change ships, AgentOS traces the call graph and returns the exact impacted set: caller sites, files, modules, downstream contracts. Pure graph traversal — no LLM, no rerank.

Source of truth

FAFO Memory's code graph index (5,447 indexed source documents in this example). Tool: trace_symbol_dependencies — direct query against code_graph_edges.

Mechanism

At indexing time, FAFO Memory walks the AST and writes a row per edge into the code graph (calls / imports / implements / references / defines / reexports). At query time, the tool reads the graph directly — no embedding lookup, no model call. Latency is dominated by PG round-trips.

Evidence
$ trace_symbol_dependencies(
    symbol = "SchemaValidator.run",
    index  = "your-codebase",
    depth  = 1,
    direction = "both"
  )

  → 14 caller sites
  → 4 files
  → 2 modules touched  (ingestion · validator)
  → 2 downstream contracts  (structural · semantic)
  → 0.4 s latency  (pure graph; no LLM, no rerank)

  BLAST RADIUS: module
  ↳ stays inside the "validator" envelope
  ↳ escalates to SYSTEM if structural::validate signature changes too
  ↳ verdict: in-envelope, no escalation required
Reproduction
Source artifact
your AST-chunked code graph (built by FAFO Memory at index time)
Command
trace_symbol_dependencies(symbol=<target>, index=<your-codebase>, depth=1, direction="both")
Expected output
edge list with source_file_path · source_start_line · source_symbol · target_symbol · edge_type · confidence
Verification
rename the target symbol on a branch; the count of files that must change should match the trace's distinct caller-file count
Caveats
Edge confidence varies. Edges are tagged exact or inferred; use min_confidence=exact for high-stakes traces. Sub-second is typical; p99 is ~2.5s on the published bench.