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fix(mcp): strip a leading UTF-8 BOM before frontmatter fence detection
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Round-5 review found a sixth bypass, same mechanism as round 4's CRLF gap,
one layer earlier: a leading UTF-8 BOM (EF BB BF) defeats
strings.HasPrefix(doc, "---\n") before CRLF normalization even applies.
Judged live-plausible rather than exotic — Notepad's default "UTF-8" save
and PowerShell's pre-v6 Out-File/Set-Content both emit a BOM — so fixed
inline at the same cost as the CRLF fix rather than deferred wholesale to
hyperguild#138.

Strip the BOM before the CRLF normalization in frontmatterBlock, so every
caller (fence-presence detection and frontmatterScalars) agrees regardless
of encoding.

Drawing the line here: further encoding variants in this family (NEL line
separators, UTF-16 BOM, lone-CR classic-Mac endings) are judged not
live-plausible in a git-tracked UTF-8 markdown corpus and are tracked
wholesale under hyperguild#138's parser consolidation rather than chased as
individual rounds on this PR.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
mathias
2026-09-23 10:44:54 +02:00
co-authored by Claude Sonnet 5
parent 4f75279ceb
commit 1d67e16c0d
2 changed files with 33 additions and 2 deletions
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ingestion/internal/mcp/tools_notes_test.go
+26
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@@ -223,6 +223,32 @@ func TestBrainEdit_RejectsAnInvalidEnvelopeOnACRLFFencedNote(t *testing.T) {
assert.Contains(t, string(got), "claim_provenance: asserted", "rejected edit must leave the note byte-identical")
}
func TestBrainEdit_RejectsAnInvalidEnvelopeOnABOMPrefixedNote(t *testing.T) {
// Found in round-5 review: the same "encoding property empties
// frontmatterScalars's map" mechanism as the CRLF bypass, one layer
// earlier — a leading UTF-8 BOM (EF BB BF) defeats
// strings.HasPrefix(doc, "---\n") exactly like CRLF did, before that
// prefix is even reached. Notepad's default "UTF-8" save and
// PowerShell's pre-v6 Out-File/Set-Content both emit a BOM, so this is
// a live, plausible authoring path, not an exotic one — same severity
// and same one-line cost as the CRLF fix, fixed the same way rather
// than deferred to hyperguild#138.
dir := newBrainRepo(t)
note := filepath.Join(dir, "wiki/homelab/facts/n.md")
require.NoError(t, os.WriteFile(note,
[]byte("\xef\xbb\xbf---\ntitle: 'n'\nhalf_life: durable\napplies: universal\nclaim_provenance: asserted\n---\n\nbody\n"), 0o644))
srv := mcp.NewServer(dir, nil, nil, nil)
resp := call(t, srv, "brain_edit", map[string]any{
"path": "wiki/homelab/facts/n.md", "old_str": "asserted", "new_str": "guessed",
})
require.Contains(t, resp, "error", "%v", resp)
got, err := os.ReadFile(note)
require.NoError(t, err)
assert.Contains(t, string(got), "claim_provenance: asserted", "rejected edit must leave the note byte-identical")
}
func TestBrainEdit_AllowsAValidClaimEnvelopeEdit(t *testing.T) {
dir := newBrainRepo(t)
note := filepath.Join(dir, "wiki/homelab/facts/n.md")