Trailmark Variant Neighborhood

---
name: trailmark-variant-neighborhood
description: "Expands one confirmed or suspected vulnerability into a Trailmark graph neighborhood of variant candidates by finding sibling functions, shared callers and callees, common sensitive sinks, common entrypoint paths, interface implementations, override relationships, type/reference neighbors, and structurally similar nodes. Use after one issue is found to seed variant-analysis, semgrep-rule-creator, static-analysis, or manual review with graph-derived candidate locations."
allowed-tools:
  - Bash
  - Read
  - Grep
  - Glob
  - Write
---

# Trailmark Variant Neighborhood

Expand one seed issue into graph-derived variant candidates. This skill
generates review targets, not confirmed findings.

## When to Use

- A finding is confirmed or plausible and variants may exist
- The vulnerable pattern depends on call context
- The issue involves a shared sink, source, validator, interface, override,
  trait, hook, handler, adapter, or critical type
- The next step is to seed `variant-analysis`, `semgrep-rule-creator`,
  `static-analysis`, or manual review

## When NOT to Use

- No seed issue exists. Use discovery or triage first.
- The pattern is purely syntactic and already obvious. Use
  `semgrep-rule-creator` directly.
- The question is exploit-chain composition across multiple findings. Use a
  composition workflow.
- The goal is remediation verification. Use a remediation-review workflow.
- The seed cannot be bound to a graph node.

## Rationalizations to Reject

| Rationalization | Why It Is Wrong | Required Action |
|---|---|---|
| "Nearby code means variant" | Proximity is only a candidate reason | Rank it as a review target |
| "Only exact same names matter" | Variants often share sinks or preconditions, not names | Expand across callers, callees, interfaces, and types |
| "Every candidate is a finding" | This skill outputs candidates for review | Avoid vulnerability claims |
| "Unreachable candidates can be ignored completely" | They may become reachable after refactors | Rank lower or list as deferred |
| "Graph candidates replace semantic pattern work" | Graph structure finds locations, not root-cause semantics | Hand off to variant-analysis, Semgrep, CodeQL, or manual review |

## Workflow

```
Variant Neighborhood Progress:
- [ ] Step 1: Normalize and bind the seed
- [ ] Step 2: Expand graph neighborhoods
- [ ] Step 3: Rank candidates
- [ ] Step 4: Extract variant pattern guidance
- [ ] Step 5: Emit handoff packet
```

### Step 1: Normalize And Bind The Seed

Accept finding text, file/line, function name, or output from
`trailmark-finding-triage`. Bind the seed to a Trailmark node and record the
root cause in plain language.

If the seed has no concrete graph binding, stop before inventing variants.

### Step 2: Expand Neighborhoods

Use the dimensions in
[references/neighborhood-patterns.md](references/neighborhood-patterns.md):

- shared callers
- shared callees and sinks
- entrypoint path neighbors
- interface, override, trait, and implementation siblings
- file or module cluster neighbors
- taint or privilege-boundary peers
- type and state-reference neighbors

Bound expansion to avoid candidate floods.

### Step 3: Rank Candidates

Rank with [references/ranking.md](references/ranking.md). Prioritize
entrypoint-reachable, tainted, boundary-adjacent, high-blast-radius, shared
sink, same-interface, and close-distance candidates. Penalize test, mock,
generated, vendor, unreachable, and trusted-internal-only candidates.

### Step 4: Extract Pattern Guidance

Summarize what should be searched for syntactically and what requires semantic
review. Identify whether follow-up belongs in:

- `variant-analysis`
- `semgrep-rule-creator`
- `static-analysis` with CodeQL or SARIF-producing tools
- manual review

### Step 5: Emit Handoff Packet

Use [references/output-format.md](references/output-format.md). Include
ranked candidates, inclusion reasons, exclusions, limitations, and the
variant-analysis handoff.

## Stop Conditions

- No graph binding exists
- Candidate count is too high and the root cause is underspecified
- Trailmark cannot analyze the target language
- The seed is only in test, generated, or vendor code and the user did not say
  that code is in scope