The headline change is `vary var`: a new top-level command that runs check, test, mutation, and review stages under a cost budget. It accepts `--dry-run --explain` to inspect the policy before spending anything, plus `--json` and `--compact` output for tools and CI. Most of the rest of the work went into mutation testing. Reachability tracing picks the tests that actually cover a mutant, kill-first scheduling runs the most likely killers first, warm workers reuse JVM processes across runs, and a pluggable backend adds method-body hot-swap with a fresh-loader fallback. A parity benchmark runs every mode side by side and fails if optimized execution classifies any mutant differently from the safer baseline.

The release also adds Frugal, a native PEG parser library ported from [Parsimonious](https://github.com/erikrose/parsimonious). Dict generic codegen brings operator overloading and interface-typed collections. `vary check` gains fourteen new rules, and `vary explain` gives plain-language descriptions of each one.

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<thead><tr style="background: rgba(0, 0, 0, 0.03);"><th style="text-align: left;">Change</th><th style="text-align: left;">Description</th></tr></thead>
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<tr><td><code>vary var</code> adaptive review loop</td><td>New top-level command that runs check, test, mutation, and review stages under a cost budget, with <code>--dry-run --explain</code>, <code>--json</code>, <code>--compact</code>, <code>--since-ref</code>, and <code>--include-mutation</code>.</td></tr>
<tr><td>Mutation engine overhaul</td><td>Reachability-traced test selection, kill-first scheduling, warm JVM workers, and a pluggable backend with method-body hot-swap and fresh-loader fallback.</td></tr>
<tr><td>Strict-mode parity benchmark</td><td>Reference, evidence, warm, and hot-swap modes are run side-by-side and fail if any mutant is classified differently from the safer baseline.</td></tr>
<tr><td>Mutation telemetry</td><td>Fine-grained execution telemetry, persisted history, survivor-tail grouping, incremental relevance inference, and validated fast mode with selection ordering in reports.</td></tr>
<tr><td><code>vary benchmark</code></td><td>New CLI command for the strict-mode parity benchmark.</td></tr>
<tr><td>Cross-language mutation benchmark</td><td>Published benchmark comparing Vary's mutation cost model against established tools.</td></tr>
<tr><td>Frugal PEG parser library</td><td>Native Vary grammar and parser library, a Parsimonious port with full upstream parity, enum-typed grammars, match dispatch, and contract-checked combinators.</td></tr>
<tr><td>Test transpilation framework</td><td>Python tests transpile to Vary via Frugal for Parsimonious parity validation.</td></tr>
<tr><td>Dict generic codegen</td><td><code>Dict[K, V]</code> lowers through generic codegen with operator overloading and interface-typed collections.</td></tr>
<tr><td>Codegen fixes</td><td>Enum codegen, variable shadowing in nested scopes, and module-level <code>var</code> initialization order.</td></tr>
<tr><td>Fourteen new <code>vary check</code> rules</td><td>Four structural rules (VCL001 - VCL004), six architecture-smell rules, plus parallel collections, hand-rolled tagged unions, stale workarounds, and mixed-concern functions.</td></tr>
<tr><td><code>vary explain</code></td><td>New CLI command that explains a rule or diagnostic in plain language with remediation guidance.</td></tr>
<tr><td>Cached-run startup perf</td><td>Stops SHA-256ing the compiler JAR on every cached run.</td></tr>
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