scenario
Decompose a feature across 12 risk dimensions → exhaustive, severity-tagged edge cases.
What this is - and isn't
| Skill |
Does |
vd:cook --tdd |
Runs the tests (tests-first), reports pass/fail |
vd:brainstorm |
Explores solution options |
scenario |
Enumerates edge cases & failure modes (default), or proves a change's safety fact by running code (--diff) - never fixes |
Default-mode output is an input to test-writing / QA / vd:plan risk sections - not executable tests. --diff is the exception: it writes and runs a small proof script, because a blast-radius verdict without executed evidence is just a persuasive paragraph.
Modes
| Mode |
Behaviour |
| (default) |
One pass over all 12 dimensions → scenario list. |
--saturation |
Iterative rounds until coverage is exhausted (2 consecutive zero-new rounds) or --iterations cap (default 5). |
--diff [ref] |
Blast-radius review of a change: what breaks beyond the diff, with the one safety fact proven by running real code. Default ref: merge-base with the default branch (uncommitted changes included). |
--iterations only applies with --saturation (default mode is a single pass).
Workflow
- Read the target - the file/function or feature description. Identify inputs, outputs, state, external calls.
- Walk the 12 dimensions - see
references/dimensions.md. For each, ask "what input/condition in this category breaks the target?"
- Emit scenarios - group by dimension; each: a one-line condition, severity (Critical/High/Med/Low), why it breaks, suggested test/assertion.
- (saturation) - repeat with a completeness critic ("which dimension or angle is still thin?"); dedupe against the seen-set; stop per the rules in
references/saturation-loop.md.
- Save the report - write to the injected
Reports: path. Filename: scenario-{date}-{slug}.md.
Final handoff must include an openable report location, such as
[scenario-report.md](/absolute/path/to/scenario-report.md) or
file:///absolute/path/to/scenario-report.md, not just the basename.
Output shape
## <dimension>
- **[High]** <condition> - breaks because <reason>. Test: <assertion>.
- **[Low]** <condition> - ...
End with a coverage line: Dimensions covered: 12/12 · scenarios: N · saturation rounds: R.
Blast-radius mode (--diff)
Default mode enumerates what could break in a design. --diff answers a sharper question about a concrete change: what does this break somewhere else, and what is the one fact it is safe because of. Listing callers is not the job - grep finds those in a second. The job is the breakage grep does not show.
- Read the change - the diff, the symbols it adds/changes/deletes, and what it now does differently, including the part the diff does not spell out.
- Find the one safety fact. Most scary-looking changes are safe because of a single fact ("this call only drops already-dead cache entries"). Find it; if it holds, most risks die at once. Spend time here, not on a long list of maybes.
- Look where grep stops - the pinned library's own source, execution timing (teardown, microtasks, retries), and what symbol search misses: API response shapes, DB columns, wire formats, feature flags, consumers three hops downstream, other languages reading the same bytes.
- Rate each risk honestly - real likelihood, real cost. Keep confirmed risks; list checked-and-cleared separately. Cite real
file:line; a search that finds nothing is still an answer; never invent a caller.
- Prove the one fact by running code - a small script or test that calls the real code and fails loud if the fact is false. Paste the output. A writeup that merely sounds right is the trap.
Certainty ladder - get every safety fact as far down as is cheap, and say where it stopped:
| Level |
Evidence |
| 1 |
You said so - worthless alone |
| 2 |
You pointed at a real file:line (or the library's own source) |
| 3 |
You walked the failure path and it cannot reach |
| 4 |
You ran a script/test against the real code |
| 5 |
You reproduced it in the running app |
A fact stuck below 4 is reported as unproven, never rounded up to settled.
Output shape (--diff): What it does (incl. the non-obvious part) · The one safety fact + its ladder level + proof output · Risks (each: how it breaks, file:line, likelihood, cost, how to check) · Cleared · Before you merge (the cheapest test that catches the real bug).
Save it like the default mode: write the report to the injected Reports: path as scenario-diff-{date}-{slug}.md and hand back an openable location (file:///absolute/path), not just the basename.
Boundaries: landing verdicts stay with vd:code-review; codebase-fit stays with vd:code-review --refactor; this mode owns beyond-the-diff breakage with runnable proof.
Limitations (honest)
- Enumeration quality depends on understanding the target - read it, don't guess.
- Not a fuzzer or property tester - default mode proposes cases without executing them; only
--diff runs code, and only to prove the named safety fact.
--saturation is bounded - it will stop at the iteration cap even if more cases theoretically exist (logs that it stopped).
1---2name: scenario3description: Generate comprehensive edge cases and test scenarios by decomposing a feature or file across 12 risk dimensions, or blast-radius review a change with --diff: what breaks beyond the diff, proven by running real code. Use for pre-implementation risk discovery, QA planning, regression design, exhaustive edge-case enumeration, and change-safety review. Triggers: 'edge cases for X', 'what could break', 'blast radius', 'what could this break beyond the diff', 'test scenarios', 'QA plan', 'risk discovery', 'enumerate failure modes'.4license: MIT5---67# scenario89> Decompose a feature across 12 risk dimensions → exhaustive, severity-tagged edge cases.1011## What this is - and isn't1213| Skill | Does |14|---|---|15| `vd:cook --tdd` | **Runs** the tests (tests-first), reports pass/fail |16| `vd:brainstorm` | Explores *solution* options |17| **`scenario`** | **Enumerates** edge cases & failure modes (default), or **proves** a change's safety fact by running code (`--diff`) - never fixes |1819Default-mode output is an input to test-writing / QA / `vd:plan` risk sections - not executable tests. `--diff` is the exception: it writes and runs a small proof script, because a blast-radius verdict without executed evidence is just a persuasive paragraph.2021## Modes2223| Mode | Behaviour |24|---|---|25| _(default)_ | One pass over all 12 dimensions → scenario list. |26| `--saturation` | Iterative rounds until coverage is exhausted (2 consecutive zero-new rounds) or `--iterations` cap (default 5). |27| `--diff [ref]` | Blast-radius review of a *change*: what breaks beyond the diff, with the one safety fact proven by running real code. Default ref: merge-base with the default branch (uncommitted changes included). |2829`--iterations` only applies with `--saturation` (default mode is a single pass).3031## Workflow32331. **Read the target** - the file/function or feature description. Identify inputs, outputs, state, external calls.342. **Walk the 12 dimensions** - see [`references/dimensions.md`](references/dimensions.md). For each, ask "what input/condition in this category breaks the target?"353. **Emit scenarios** - group by dimension; each: a one-line condition, **severity** (Critical/High/Med/Low), why it breaks, suggested test/assertion.364. **(saturation)** - repeat with a completeness critic ("which dimension or angle is still thin?"); dedupe against the seen-set; stop per the rules in [`references/saturation-loop.md`](references/saturation-loop.md).375. **Save** the report - write to the injected `Reports:` path. Filename: `scenario-{date}-{slug}.md`.38 Final handoff must include an openable report location, such as39 `[scenario-report.md](/absolute/path/to/scenario-report.md)` or40 `file:///absolute/path/to/scenario-report.md`, not just the basename.4142## Output shape4344```markdown45## <dimension>46- **[High]** <condition> - breaks because <reason>. Test: <assertion>.47- **[Low]** <condition> - ...48```4950End with a coverage line: `Dimensions covered: 12/12 · scenarios: N · saturation rounds: R`.5152## Blast-radius mode (`--diff`)5354Default mode enumerates what *could* break in a design. `--diff` answers a sharper question about a concrete change: what does this break somewhere else, and what is the one fact it is safe because of. Listing callers is not the job - grep finds those in a second. The job is the breakage grep does not show.55561. **Read the change** - the diff, the symbols it adds/changes/deletes, and what it now does differently, including the part the diff does not spell out.572. **Find the one safety fact.** Most scary-looking changes are safe because of a single fact ("this call only drops already-dead cache entries"). Find it; if it holds, most risks die at once. Spend time here, not on a long list of maybes.583. **Look where grep stops** - the pinned library's own source, execution timing (teardown, microtasks, retries), and what symbol search misses: API response shapes, DB columns, wire formats, feature flags, consumers three hops downstream, other languages reading the same bytes.594. **Rate each risk honestly** - real likelihood, real cost. Keep confirmed risks; list checked-and-cleared separately. Cite real `file:line`; a search that finds nothing is still an answer; never invent a caller.605. **Prove the one fact by running code** - a small script or test that calls the real code and fails loud if the fact is false. Paste the output. A writeup that merely sounds right is the trap.6162**Certainty ladder** - get every safety fact as far down as is cheap, and say where it stopped:6364| Level | Evidence |65|---|---|66| 1 | You said so - worthless alone |67| 2 | You pointed at a real `file:line` (or the library's own source) |68| 3 | You walked the failure path and it cannot reach |69| 4 | You ran a script/test against the real code |70| 5 | You reproduced it in the running app |7172A fact stuck below 4 is reported as **unproven**, never rounded up to settled.7374**Output shape (`--diff`):** What it does (incl. the non-obvious part) · The one safety fact + its ladder level + proof output · Risks (each: how it breaks, `file:line`, likelihood, cost, how to check) · Cleared · Before you merge (the cheapest test that catches the real bug).7576**Save it like the default mode:** write the report to the injected `Reports:` path as `scenario-diff-{date}-{slug}.md` and hand back an openable location (`file:///absolute/path`), not just the basename.7778**Boundaries:** landing verdicts stay with `vd:code-review`; codebase-fit stays with `vd:code-review --refactor`; this mode owns beyond-the-diff breakage with runnable proof.7980## Limitations (honest)8182- Enumeration quality depends on understanding the target - read it, don't guess.83- Not a fuzzer or property tester - default mode proposes cases without executing them; only `--diff` runs code, and only to prove the named safety fact.84- `--saturation` is bounded - it will stop at the iteration cap even if more cases theoretically exist (logs that it stopped).
vanducng