chore(brain): remove brain_write legacy params domain/type/knowledge-path (ADR-0012)

hyperguild#79's caller audit (done in a prior session) found the removal
was safe:

- The promote/pending flow (#38/#81, ingestion/internal/api/promote.go)
  operates exclusively on brainDir/raw/ -> brainDir/wiki/<wing>/<hall>/. It
  never touches brainDir/knowledge/, so removing the knowledge/ write path
  does not break it.
- No live caller uses domain/type or the knowledge/ path: checked
  hyperguild itself, mathias/skills, mathias/agentsquad, mathias/dispatch,
  mathias/cad, mathias/cad-atlas.
- internal/skills/brain (a skill.go + handlers.go pair) defined a third,
  even-more-legacy brain_write shape (type/domain/filename, no wing/hall)
  for an old "supervisor" MCP server whose cmd/supervisor/main.go no
  longer exists. Nothing outside its own test imported it; deleted
  entirely as it encodes the exact legacy shape this issue removes.

Changes:
- ingestion/internal/mcp/handlers.go: brain_write's tool schema and
  brainWriteArgs drop type/domain; wing+hall are now marked required in
  the schema.
- ingestion/internal/api/handler.go: WriteNote has one behaviour — wing+
  hall required, routing to wiki/<wing>/<hall>/. writeLegacyNote and the
  knowledge/-path branch are deleted. Omitting wing or hall now returns
  "wing and hall are required" (400 over HTTP, a tool error over MCP) —
  the only sane failure mode left once there is no other valid
  destination.
- ingestion/internal/capture/ports.go, internal/brainstore/store.go: drop
  Type/Domain from capture.Note and its WriteNoteOptions construction.
  pipeline/*.go's unrelated "domain" field (a different, legitimate
  concept for brain_ingest_raw) is untouched.
- internal/skills/brain/: deleted (orphaned legacy tool schema, dead
  since cmd/supervisor was removed).

Tests: added TestWriteNote_RequiresWingAndHall (api),
TestBrainWriteRequiresWingAndHall +
TestBrainWriteIgnoresLegacyTypeAndDomainParams (mcp) for the new single
behaviour; removed tests that only exercised the deleted legacy path
(TestWrite_IncludesFrontmatterWhenTypeProvided,
TestWriteNote_HallRouteExistingTypeWinsOverOptsType,
TestBrainWriteRejectsTraversal, TestBrainWriteAcceptsDoubleDotInName —
the latter two's filename-sanitisation behaviour is covered independently
by internal/brain/path_test.go's TestNotePath_SanitisesWingAndSlug /
TestSanitise, which is unaffected by this change).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

ingestion/internal/api/handler.go

@@ -54,8 +54,6 @@ type queryRequest struct {
 type writeRequest struct {
 	Content    string `json:"content"`
 	Filename   string `json:"filename,omitempty"`
-	Type       string `json:"type,omitempty"`
-	Domain     string `json:"domain,omitempty"`
 	Wing       string `json:"wing,omitempty"`
 	Hall       string `json:"hall,omitempty"`
 	SourceType string `json:"source_type,omitempty"` // "external" opts a hall=facts entry out of the internal default
@@ -110,17 +108,13 @@ func (h *Handler) Query(w http.ResponseWriter, r *http.Request) {
 
 // WriteNoteOptions configures how a brain note is written.
 //
-// When both Wing and Hall are non-empty, the note routes into the
-// structured wiki at brain/wiki/<wing>/<hall>/<slug>.md and gets
-// wing/hall/created_at injected into its YAML frontmatter.
-//
-// When either is empty, the note falls back to brain/knowledge/<filename>
-// with optional type/domain frontmatter (legacy behaviour).
+// Wing and Hall are both required: the note routes into the structured
+// wiki at brain/wiki/<wing>/<hall>/<slug>.md and gets wing/hall/created_at
+// injected into its YAML frontmatter. There is no other valid destination
+// (the legacy brain/knowledge/ fallback was removed — ADR-0012 / #79).
 type WriteNoteOptions struct {
 	Content    string
 	Filename   string
-	Type       string
-	Domain     string
 	Wing       string
 	Hall       string
 	SourceType string // "internal" marks a first-party observation (e.g. claudewatcher) that needs no external citation
@@ -132,6 +126,9 @@ func WriteNote(brainDir string, opts WriteNoteOptions) (string, error) {
 	if opts.Content == "" {
 		return "", fmt.Errorf("content is required")
 	}
+	if opts.Wing == "" || opts.Hall == "" {
+		return "", fmt.Errorf("wing and hall are required")
+	}
 
 	// In the primitive, not in a caller: POST /write reaches here directly,
 	// without the BrainStore, and a gate one door wide is not a gate.
@@ -143,13 +140,7 @@ func WriteNote(brainDir string, opts WriteNoteOptions) (string, error) {
 	}
 	opts.Content = clean
 
-	if opts.Wing != "" && opts.Hall != "" {
-		return writeHallNote(brainDir, opts)
-	}
-	if opts.Wing != "" || opts.Hall != "" {
-		return "", fmt.Errorf("wing and hall must be set together")
-	}
-	return writeLegacyNote(brainDir, opts)
+	return writeHallNote(brainDir, opts)
 }
 
 // writeHallNote routes a note into brain/wiki/<wing>/<hall>/ and injects
@@ -207,9 +198,6 @@ func writeHallNote(brainDir string, opts WriteNoteOptions) (string, error) {
 			fmt.Fprintf(&fm, "%s: %s\n", key, fallback)
 		}
 	}
-	writeField("type", opts.Type)
-	writeField("domain", opts.Domain)
-
 	sourceType := opts.SourceType
 	if sourceType == "" && opts.Hall == "facts" {
 		// Most hall=facts entries are first-party (an eval/benchmark the
@@ -300,53 +288,7 @@ func splitFrontmatter(content string) (fields []frontmatterField, body string) {
 	return fields, body
 }
 
-// writeLegacyNote preserves the original brain/knowledge/ behaviour for
-// callers that have not adopted the wing/hall taxonomy.
-func writeLegacyNote(brainDir string, opts WriteNoteOptions) (string, error) {
-	filename := opts.Filename
-	if filename == "" {
-		filename = fmt.Sprintf("%s-auto.md", time.Now().UTC().Format("2006-01-02-150405"))
-	}
-
-	rawDir := filepath.Join(brainDir, "knowledge")
-	if err := os.MkdirAll(rawDir, 0o755); err != nil {
-		return "", fmt.Errorf("create raw dir: %w", err)
-	}
-
-	finalContent := opts.Content
-	if opts.Type != "" || opts.Domain != "" {
-		var fm strings.Builder
-		fm.WriteString("---\n")
-		if opts.Type != "" {
-			fmt.Fprintf(&fm, "type: %s\n", opts.Type)
-		}
-		if opts.Domain != "" {
-			fmt.Fprintf(&fm, "domain: %s\n", opts.Domain)
-		}
-		fm.WriteString("---\n")
-		finalContent = fm.String() + opts.Content
-	}
-
-	if strings.ContainsAny(filename, `/\`) {
-		return "", fmt.Errorf("invalid filename")
-	}
-	base := filepath.Base(filename)
-	if base == "." || base == ".." || base == "" {
-		return "", fmt.Errorf("invalid filename")
-	}
-	if !strings.HasSuffix(base, ".md") {
-		base += ".md"
-	}
-	dest := filepath.Join(rawDir, base)
-	if err := os.WriteFile(dest, []byte(finalContent), 0o644); err != nil {
-		return "", fmt.Errorf("write: %w", err)
-	}
-
-	rel, _ := filepath.Rel(brainDir, dest)
-	return filepath.ToSlash(rel), nil
-}
-
-// Write handles POST /write — write raw content to brain/knowledge/.
+// Write handles POST /write — write a note into brain/wiki/<wing>/<hall>/.
 func (h *Handler) Write(w http.ResponseWriter, r *http.Request) {
 	var req writeRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
@@ -359,10 +301,10 @@ func (h *Handler) Write(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
-	if req.Wing != "" && req.Hall != "" {
-		if err := brain.BuildWingIndex(h.brainDir, req.Wing); err != nil {
-			h.logger.Warn("auto-index failed", "wing", req.Wing, "err", err)
-		}
+	// WriteNote errors out above unless both are set, so this always runs —
+	// no legacy fallback path left to guard against.
+	if err := brain.BuildWingIndex(h.brainDir, req.Wing); err != nil {
+		h.logger.Warn("auto-index failed", "wing", req.Wing, "err", err)
 	}
 	writeJSON(w, map[string]string{"path": relPath})
 }