diff --git a/README.md b/README.md
index a4147ab..9c94308 100644
--- a/README.md
+++ b/README.md
@@ -127,10 +127,12 @@ in each. `test/packaging/lint-once.test.ts` asserts that count by walking the
 invocation graph, so a second pass cannot creep back in unnoticed.
 
 `script/fmt-check` remains as a standalone entrypoint for asking the formatting
-question on its own, without docker and without the rest of lint. It is the one
-formatting path that still runs on the host, and nothing reaches it: neither
-`script/check` nor `script/precommit` calls it, so it never contributes to their
-verdicts. Its own verdict cannot drift from the container's: prettier is pinned
+question on its own, without docker and without the rest of lint. It is not the
+last formatting path on the host — `script/fmt` writes with the host prettier,
+and `package.json` exposes `fmt` and `fmt-check` as direct prettier calls — it is
+the one of them that the check graph could plausibly have reached, and nothing
+reaches it: neither `script/check` nor `script/precommit` calls it, so it never
+contributes to their verdicts. Its own verdict cannot drift from the container's: prettier is pinned
 to an exact version, installed from `yarn.lock` under `--frozen-lockfile` in
 both places, and reads `.gitignore` as its default ignore file — which is why
 `.dockerignore` deliberately keeps `.gitignore` in the build context.
diff --git a/test/packaging/lint-once.test.ts b/test/packaging/lint-once.test.ts
index 895bb6b..7b2c4bf 100644
--- a/test/packaging/lint-once.test.ts
+++ b/test/packaging/lint-once.test.ts
@@ -40,12 +40,18 @@
 // value built by a make function (`$(shell ...)`, `$(addprefix ...)`), and the
 // body of a `define`/`endef` block are not expanded and not followed. A
 // `docker build` resolves to the file named by `-f`, `-f=`, `-f<file>` with
-// the value attached to the flag, `--file` or `--file=`, wherever in the
-// invocation that flag sits, and to `Dockerfile` when it names none; a
+// the value attached to the flag, `--file` or `--file=`, wherever in that
+// invocation the flag sits, and to `Dockerfile` when it names none; a
 // Dockerfile chosen some other way — a bundled short flag cluster
 // (`-qf <file>`), a value this walk cannot expand to a literal — resolves to
-// the default rather than to the real file. Within those edges, a
-// prettier call is caught wherever it is added.
+// the default rather than to the real file. Each `docker build` on a line is
+// followed separately, and the flag search for one is bounded to the slice
+// running from that command to the next `&&`, `||`, `;` or `|`, so a second
+// build on the same line is not swallowed by the first and a later command's
+// `-f` is not read as the build's. That bounding is a split on those four
+// separators, not a shell parse: a separator appearing inside quotes or a
+// command substitution still ends the slice. Within those edges, a prettier
+// call is caught wherever it is added.
 //
 // Two entrypoints are walked, because they cover different graphs: `make check`
 // is what a developer runs, and `.gitea/workflows/check.yml` is what CI runs.
@@ -58,8 +64,9 @@
 // Undercounting is the failure mode that would make this test worthless. Three
 // things guard against it: the walk is asserted to have reached the nodes that
 // matter, an unresolvable or empty node is a thrown error rather than a quiet
-// zero, and prettier is counted per occurrence rather than per line, so two
-// invocations chained with `&&` cannot read as one.
+// zero, and both the counting and the edge-following are per occurrence rather
+// than per line, so two prettier calls or two `docker build`s chained with `&&`
+// on one line cannot read as one.
 import { describe, expect, it } from "vitest";
 import { readFileSync } from "node:fs";
 import { fileURLToPath } from "node:url";
@@ -449,8 +456,24 @@ const edgesOf = (line: string): string[] => {
     // the same letters cannot supply the match, and the attached form is
     // allowed only for the short flag, so that `--force-rm` — a long flag that
     // merely starts with the same letters — still does not read as one.
-    if (/\bdocker\s+build\b/.test(line)) {
-        const file = /\s(?:--file[=\s]+|-f=?\s*)(\S+)/.exec(line);
+    //
+    // Every `docker build` on the line produces an edge, and each one looks for
+    // its file flag only within its own invocation — the slice from the command
+    // to the next `&&`, `||`, `;` or `|`. One `test` and one `exec` over the
+    // whole line got both halves of that wrong: `docker build -f Dockerfile.lint
+    // . && docker build -f Dockerfile.extra .` followed the first file and
+    // dropped the second, so a tree running prettier twice reported green, and a
+    // bare `docker build . && cp -f Dockerfile.lint /tmp/x` read `cp`'s `-f` as
+    // the build's, counting an invocation that never happens and losing the
+    // default `Dockerfile` edge. The bounding is a split on those four
+    // separators and nothing more: a separator inside quotes or a `$(...)`
+    // substitution ends the slice anyway, and a newline-separated command list
+    // is already one line per invocation by the time it gets here.
+    for (const match of line.matchAll(/\bdocker\s+build\b/g)) {
+        const invocation = line
+            .slice(match.index)
+            .split(/&&|\|\||;|\|/)[0] as string;
+        const file = /\s(?:--file[=\s]+|-f=?\s*)(\S+)/.exec(invocation);
         edges.push(`docker:${file === null ? "Dockerfile" : file[1]}`);
     }