diff --git a/code-languages/bash.md b/code-languages/bash.md
index d843a53..896bf5f 100644
--- a/code-languages/bash.md
+++ b/code-languages/bash.md
@@ -125,6 +125,10 @@ mistakes before a human does.
 - **A skipped test fails the gate.** Never let a skip report green.
 - **Print a summary with numbers**, not just a verdict — counts of warnings, suppressions, and
   file-size violations. A suppression count that has grown is worth seeing even on a pass.
+- **Don't reimplement in the gate what a test can assert.** Checks like file-size limits
+  belong in the test suite where they travel with the repo and fail with a useful message;
+  the build script is the fallback for projects with no suite to hang them on. See
+  [`coding-dev.md` §4](skills-public/coding-dev.md).
 - Keep per-step logs in a known directory so a failure can be read after the fact.
 - **Never bypass a failed gate** by copying a binary or running the install step by hand. Fix
   the failing step; do not weaken the check to make it pass.
diff --git a/code-languages/csharp-dotnet.md b/code-languages/csharp-dotnet.md
index 3bb1ca9..866357b 100644
--- a/code-languages/csharp-dotnet.md
+++ b/code-languages/csharp-dotnet.md
@@ -80,7 +80,8 @@ dotnet build MySolution.sln -warnaserror
 - Pattern matching and switch expressions over `if`/`else` ladders.
 - `IReadOnlyList<T>` / `IReadOnlyDictionary<K,V>` in public signatures returning collections.
 - `internal` by default; `public` only for genuine API surface.
-- File and function size limits from the general rules apply.
+- File and function size limits from the general rules apply — put the file limit in a test
+  rather than an MSBuild target (see [`coding-dev.md` §4](skills-public/coding-dev.md)).
 - `dotnet format` before committing.
 
 ---
diff --git a/code-languages/go.md b/code-languages/go.md
index bb24de6..9303b39 100644
--- a/code-languages/go.md
+++ b/code-languages/go.md
@@ -137,7 +137,8 @@ CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o bin/app ./cmd/app
 - Keep the exported surface small. Unexported by default.
 - Embed frontend/static assets with `//go:embed` for single-binary distribution — the frontend
   itself follows [`js-typescript.md`](skills-public/code-languages/js-typescript.md).
-- File and function size limits from the general rules apply.
+- File and function size limits from the general rules apply — `funlen` in `golangci-lint`
+  covers functions; put the file limit in a test (see [`coding-dev.md` §4](skills-public/coding-dev.md)).
 
 ---
 
diff --git a/code-languages/js-typescript.md b/code-languages/js-typescript.md
index bbee280..038a56a 100644
--- a/code-languages/js-typescript.md
+++ b/code-languages/js-typescript.md
@@ -141,7 +141,8 @@ Attach an `AbortController` to every long-lived `fetch` and abort it in cleanup.
   a new formatter or lint config into a project that already has one.
 - **One file until it earns a split** — around 250 lines for a self-contained plugin/feature,
   or when a second file is genuinely reusable (`utils.ts`, `types.ts`, `components/`).
-  Hard limits from the general rules still apply.
+  Hard limits from the general rules still apply: ESLint's `max-lines` and
+  `max-lines-per-function` cover both natively, so prefer those over a separate test here.
 
 ---
 
diff --git a/code-languages/python.md b/code-languages/python.md
index 649f3cc..8d77808 100644
--- a/code-languages/python.md
+++ b/code-languages/python.md
@@ -132,7 +132,9 @@ When talking to a rate-limited API (a chat platform, a store, a tracker):
   installable package** with its own repo and version, consumed as a dependency.
 - Keep persistent state in the framework's own config/storage system so it survives restarts;
   do not invent a parallel JSON file beside it.
-- File and function size limits from the general rules apply.
+- File and function size limits from the general rules apply — Ruff's `PLR0915` covers
+  function length; put the file limit in a pytest case (see
+  [`coding-dev.md` §4](skills-public/coding-dev.md)).
 
 ---
 
diff --git a/code-languages/rust.md b/code-languages/rust.md
index 92a04cd..2b869f4 100644
--- a/code-languages/rust.md
+++ b/code-languages/rust.md
@@ -75,6 +75,10 @@ workspace = true
 - **Re-test every `#[allow]` periodically.** If removing one produces no warning, delete it.
 - `too_many_lines` is the mechanical enforcement of the 100-line function limit. A function
   that trips it wants extracting, not an allow.
+- Clippy has **no file-length lint**, so the 1000-line file limit belongs in a test — see
+  [`coding-dev.md` §4](skills-public/coding-dev.md) for the pattern. Put it in the workspace
+  root's `tests/` so one test covers every member crate, walking `src/` plus each
+  `crates/*/src`. `cargo test --workspace` then enforces it for free.
 
 ---
 
diff --git a/coding-dev.md b/coding-dev.md
index 5d18605..6af38c3 100644
--- a/coding-dev.md
+++ b/coding-dev.md
@@ -142,10 +142,49 @@ depends on those.
 | **Function parameters** | 3–4 | — | ~5, then pass a struct/object |
 | **Nesting depth** | 2 | — | 3, then extract |
 
-- **Enforce the function limit with the linter, not by eye** (e.g. Clippy's `too_many_lines`).
-  A function that trips it wants extracting, not a suppression.
-- **Enforce the file limit in the build script** — a check that fails over the hard limit and
-  *names* anything past the soft split point, so the seam gets found while splitting is cheap.
+### Enforce both mechanically, never by eye
+
+A limit nobody checks is a suggestion. Pick the **highest** applicable option:
+
+1. **A linter rule**, where one exists — the function limit is usually covered natively
+   (Clippy's `too_many_lines`, ESLint's `max-lines-per-function`, `golangci-lint`'s `funlen`,
+   Ruff's `PLR0915`). A function that trips it wants extracting, not a suppression.
+2. **A test**, for anything the linter does not cover — file length almost always falls here.
+   A test is the best home for it: it runs with the suite everyone already runs, it needs no
+   extra tooling, it fails with a message naming the offending files, and it travels with the
+   repository rather than living in one machine's shell script.
+3. **The build script**, only as a fallback when the project has no test suite to hang it on.
+
+Whichever you use, it should **fail over the hard limit** and separately *name* anything past
+the soft split point — so the seam gets found while splitting is still cheap, rather than at
+the moment the hard limit finally trips.
+
+```rust
+#[test]
+fn no_source_file_exceeds_limits() {
+    const HARD: usize = 1000;
+    const WARN: usize = 600;
+    let mut over = Vec::new();
+
+    for path in source_files() {
+        let lines = std::fs::read_to_string(&path).unwrap().lines().count();
+        if lines > HARD {
+            over.push(format!("{} — {lines} lines (limit {HARD})", path.display()));
+        } else if lines > WARN {
+            // Not a failure: surfaces the seam while splitting is still cheap.
+            eprintln!("note: {} is {lines} lines, approaching the {HARD} limit", path.display());
+        }
+    }
+
+    assert!(over.is_empty(), "files over the size limit:\n{}", over.join("\n"));
+}
+```
+
+> [!NOTE]
+> A test runs with the suite, not on every compile. If you genuinely need the check on every
+> build, most toolchains have a pre-build hook for it (Cargo's `build.rs`, an MSBuild target,
+> a bundler plugin) — but that cost is paid on every incremental build forever, and the suite
+> is usually soon enough. Reach for the hook only if oversized files keep landing anyway.
 - **Split by concern, never by line count.** A large `strip.rs` becomes
   `strip/fader.rs`, `strip/knobs.rs`, `strip/routing.rs` — never `strip1.rs` / `strip2.rs`.
 - One coherent responsibility per module. A module that draws widgets should not also own