test: fail when CLAUDE.md's line-count figures drift from the source

A CLAUDE.md `(~Nk lines)` figure exists to set expectations before you open a
file — "this is the big one, expect to navigate it" — and it drifts in total
silence, because a stale number reads exactly like a fresh one. The
2026-09-19 sweep found EVERY such figure in the workspace stale, all of them
undercounts, the worst by 49%. Nothing had noticed in months.

The test parses its own CLAUDE.md for those figures, resolves each name to a
file under src/ (a path outright, else a unique basename), and fails outside
a 10% tolerance. The failure prints the number to write, so the fix is a
paste. It also checks "largest file" where a figure claims it, and refuses to
pass when it finds NO figure at all — otherwise rewording the docs would
silently disarm it.

The first thing it caught here was an ambiguity, not a drift: the module map
said `layout.rs`, and there are two — src/layout.rs at 6853 lines and
src/scene/layout.rs at 863. The entry means the former, so it now says
`src/layout.rs`. A bare basename in a module map is fine until the name
repeats, and then it silently points at either.

Checked against deliberate breakage rather than trusted green: a restored
stale figure, a false "largest file", and a deleted figure each fail with
their own message.

Deliberately MIRRORED into each crate that carries a figure rather than
shared from a helper: every crate here is its own git repository that must
build standalone, and this needs nothing but std. Same call ramp.rs makes
about its cce-ui parser.

Co-Authored-By: Claude Opus 5 <[email protected]>

 CLAUDE.md  |   2 +-
 src/lib.rs | 142 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 143 insertions(+), 1 deletion(-)

diff --git a/CLAUDE.md b/CLAUDE.md
index d0849c7..f349101 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -328,7 +328,7 @@ cce-system-interface) to confirm behavior, not just the test suite.
 
 ## Module map (where things live)
 
-- `layout.rs` (largest file, ~6.9k lines) — fonts + sizing; many `*_font_parsed()` getters and
+- `src/layout.rs` (largest file, ~6.9k lines) — fonts + sizing; many `*_font_parsed()` getters and
   the `read_preferred_fonts` / font-family resolution used by the cosmic-text path.
 - `color.rs` — color model and named colors (`colors` re-export module in `lib.rs`).
 - `config.rs` — KDL loading and `kdl_to_json` conversion (see workspace `CLAUDE.md` for paths).
diff --git a/src/lib.rs b/src/lib.rs
index 1f316ea..ec9ee31 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -292,3 +292,145 @@ fn build_font_system(load_system_fonts: bool) -> cosmic_text::FontSystem {
 }
 
 
+
+/// CLAUDE.md's `(~Nk lines)` figures, checked against the files they describe.
+///
+/// Those numbers exist to set expectations before opening a file — "this is
+/// the big one" — and they drift in total silence, because a stale number
+/// reads exactly like a fresh one. A workspace sweep on 2026-09-19 found
+/// EVERY size figure in every CLAUDE.md stale, all of them undercounts, the
+/// worst by 49% (cce-designer's app.rs, written ~5.4k at 8046 lines).
+///
+/// Tolerance is 10%: loose enough that ordinary work does not trip it, tight
+/// enough that a file cannot quietly double. When it fails, write the number
+/// it reports — that is the whole fix.
+///
+/// Deliberately MIRRORED into each crate that carries such a figure rather
+/// than shared from a helper: every crate here is its own git repository and
+/// must build standalone, and this needs nothing but `std`. Same call
+/// `ramp.rs` makes about its cce-ui parser.
+#[cfg(test)]
+mod doc_size_claims {
+    use std::path::{Path, PathBuf};
+
+    /// One `(~Nk lines)` claim: the name as CLAUDE.md spells it, the figure,
+    /// and whether the claim also calls it the largest file.
+    fn claims(doc: &str) -> Vec<(String, f64, bool)> {
+        const TAIL: &str = " lines)";
+        let mut out = Vec::new();
+        let mut i = 0;
+        while let Some(p) = doc[i..].find(TAIL) {
+            let end = i + p;
+            i = end + TAIL.len();
+            let Some(open) = doc[..end].rfind('(') else { continue };
+            let inner = &doc[open + 1..end];
+            // "~8k", or "largest file, ~6.9k" — take the last word.
+            let largest = inner.contains("largest file");
+            let word = inner.rsplit([' ', ',']).next().unwrap_or("").trim();
+            let digits = word.trim_start_matches('~');
+            let value = match digits.strip_suffix('k') {
+                Some(k) => k.parse::<f64>().ok().map(|v| v * 1000.0),
+                None => digits.parse::<f64>().ok(),
+            };
+            // The backticked name immediately before the parenthetical.
+            let before = &doc[..open];
+            let name = before.rfind('`').and_then(|e| {
+                before[..e].rfind('`').map(|s| before[s + 1..e].to_string())
+            });
+            if let (Some(v), Some(n)) = (value, name) {
+                if v > 0.0 {
+                    out.push((n, v, largest));
+                }
+            }
+        }
+        out
+    }
+
+    /// Every `.rs` file under `src/`, as (path, line count).
+    fn sources(root: &Path) -> Vec<(PathBuf, usize)> {
+        fn walk(dir: &Path, out: &mut Vec<(PathBuf, usize)>) {
+            let Ok(entries) = std::fs::read_dir(dir) else { return };
+            for e in entries.flatten() {
+                let p = e.path();
+                if p.is_dir() {
+                    walk(&p, out);
+                } else if p.extension().and_then(|x| x.to_str()) == Some("rs") {
+                    if let Ok(s) = std::fs::read_to_string(&p) {
+                        out.push((p, s.lines().count()));
+                    }
+                }
+            }
+        }
+        let mut v = Vec::new();
+        walk(&root.join("src"), &mut v);
+        v
+    }
+
+    #[test]
+    fn test_claude_md_line_counts_match_the_source() {
+        let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+        let doc = std::fs::read_to_string(root.join("CLAUDE.md"))
+            .expect("CLAUDE.md is missing next to Cargo.toml");
+        let files = sources(root);
+        let claims = claims(&doc);
+        assert!(
+            !claims.is_empty(),
+            "no `(~N lines)` figure found in CLAUDE.md — either the syntax changed \
+             and this scan needs updating, or the figures were removed and so \
+             should this test"
+        );
+
+        let mut bad: Vec<String> = Vec::new();
+        for (name, claimed, largest) in &claims {
+            // A path relative to the crate root, else a unique basename.
+            let hits: Vec<&(PathBuf, usize)> = if root.join(name).is_file() {
+                files.iter().filter(|(p, _)| *p == root.join(name)).collect()
+            } else {
+                files
+                    .iter()
+                    .filter(|(p, _)| p.file_name().and_then(|x| x.to_str()) == Some(name.as_str()))
+                    .collect()
+            };
+            let [(path, actual)] = hits[..] else {
+                bad.push(format!("`{name}`: names {} files under src/, cannot check", hits.len()));
+                continue;
+            };
+            let actual = *actual as f64;
+            let drift = (actual - claimed) / claimed;
+            if drift.abs() > 0.10 {
+                bad.push(format!(
+                    "`{name}` is documented as ~{} lines but has {} ({:+.0}%) — write ~{}",
+                    round_k(*claimed),
+                    actual as usize,
+                    drift * 100.0,
+                    round_k(actual)
+                ));
+            }
+            if *largest {
+                if let Some((big, n)) = files.iter().max_by_key(|(_, n)| *n) {
+                    if big != path {
+                        bad.push(format!(
+                            "`{name}` is called the largest file, but {} has {n} lines",
+                            big.strip_prefix(root).unwrap_or(big).display()
+                        ));
+                    }
+                }
+            }
+        }
+        assert!(bad.is_empty(), "CLAUDE.md size claims are stale:\n  {}", bad.join("\n  "));
+    }
+
+    /// "~8k" for 8046, "~3.1k" for 3134, "~950" for 950 — the spelling the
+    /// docs already use, so the failure message can be pasted straight in.
+    fn round_k(n: f64) -> String {
+        if n < 1000.0 {
+            return format!("{}", n.round() as usize);
+        }
+        let k = n / 1000.0;
+        if (k - k.round()).abs() < 0.05 {
+            format!("{}k", k.round() as usize)
+        } else {
+            format!("{k:.1}k")
+        }
+    }
+}