---
name: logic-explain
description: >
  Explain what a specific piece of code actually does for a given input by
  producing a step-by-step execution trace (interprocedural, with name
  resolution and type transitions). Trigger when the user is confused
  about behavior or asks why code produces X instead of Y — "walk me
  through this", "trace through X with input Y", "why does this return
  X", "what does yield-from do here", "explain the execution path".
  SCOPE HARD RULE: a specific function + a specific input scenario. If the
  user wants to find bugs without a scenario in mind, use logic-review;
  two-version comparison uses logic-diff; concrete failures use
  logic-locate; codebase-wide audit uses logic-health.
  Do NOT trigger for: finding bugs without a behavioral question, style
  or design discussion, or concept explanations not tied to specific code.
---

# Logic-Lens — Execution Explain

## Setup

Read in this order:
1. `../_shared/common.md` — language rule, Report Template (Logic Score line is omitted for this mode), Remedy discipline (used only if the explanation surfaces a bug worth fixing).
2. `../_shared/semiformal-guide.md` — full tracing methodology and Premises Construction Checklist.
3. `logic-explain-guide.md` — explanation process.

Note: `logic-risks.md` is intentionally skipped — logic-explain does not produce L-code findings; if the trace reveals a bug, stop and recommend logic-review or logic-locate instead of tagging L-codes inside an explanation.

## Process

**Step 0. Language + scope routing.** Detect language per `common.md` §1. Confirm a single function + a single input scenario. If the user wants bug-finding without a scenario, hand off to logic-review.

**Step 1. Entry point and scenario** (guide Step 1) — name the function, the input scenario, and what the user is trying to understand.

**Step 2. Build premises** (guide Step 2) — resolve every non-obvious name, state the types of key variables at entry, note global/module state accessed.

**Step 3. Produce step-by-step trace** (guide Step 3) — numbered, interprocedural, active voice; cross function boundaries whenever relevant.

**Step 4. Highlight non-obvious behavior** (guide Step 4) — name resolutions, implicit coercions, hidden side effects; the "gotchas" the casual reader would miss.

**Step 5. Summarize actual vs. assumed** (guide Step 5) — one sentence each; this is the core value for the user.

**Mode line in report:** `Execution Explain` (Chinese: `执行解释`).

**Note:** Execution Explain is descriptive, not evaluative. Omit the Logic Score / Fault Confidence / Verdict line from the report header.