fix(conflict): extract fenced file content from chatty LLM resolution replies

internal/engine/conflict_extract_test.go

@@ -0,0 +1,35 @@
+package engine
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestExtractResolvedFileContent(t *testing.T) {
+	// The exact shape that corrupted a real client build's package.json: the
+	// model returned conversational preamble + a fenced block + postamble.
+	chatty := "Resolved. Kept `@playwright/test` (HEAD) — needed by test:e2e.\n\n" +
+		"Write blocked on permission. File content to apply:\n\n" +
+		"```json\n{\n  \"name\": \"isiqalo-pos-frontend\",\n  \"private\": true\n}\n```\n\n" +
+		"Grant write to apply, or paste yourself."
+	got := extractResolvedFileContent(chatty)
+	want := "{\n  \"name\": \"isiqalo-pos-frontend\",\n  \"private\": true\n}"
+	if got != want {
+		t.Fatalf("expected only the fenced JSON, got:\n%q", got)
+	}
+	if strings.Contains(got, "Resolved.") || strings.Contains(got, "Grant write") || strings.Contains(got, "```") {
+		t.Fatalf("extracted content still contains chatter/fences:\n%q", got)
+	}
+
+	// A clean response (no fence) passes through unchanged.
+	clean := "package main\n\nfunc main() {}\n"
+	if g := extractResolvedFileContent(clean); strings.TrimSpace(g) != strings.TrimSpace(clean) {
+		t.Fatalf("clean content altered: %q", g)
+	}
+
+	// A response that is ONLY a fenced block (no chatter) still yields its body.
+	fenced := "```go\npackage x\n```"
+	if g := extractResolvedFileContent(fenced); g != "package x" {
+		t.Fatalf("fenced-only extraction failed: %q", g)
+	}
+}

internal/engine/conflict_resolver.go

@@ -355,7 +355,7 @@ File: %s
 		return "", err
 	}
 
-	resolved := stripCodeFences(resp.Content)
+	resolved := extractResolvedFileContent(resp.Content)
 
 	// Sanity check: resolved content must not contain conflict markers.
 	if strings.Contains(resolved, "<<<<<<<") || strings.Contains(resolved, ">>>>>>>") {
@@ -431,7 +431,7 @@ CRITICAL OUTPUT RULES:
 		return "", err
 	}
 
-	resolved := stripCodeFences(resp.Content)
+	resolved := extractResolvedFileContent(resp.Content)
 
 	if strings.Contains(resolved, "<<<<<<<") || strings.Contains(resolved, ">>>>>>>") {
 		return "", fmt.Errorf("tech lead output still contains conflict markers")
@@ -508,6 +508,26 @@ func truncateConflictContent(content string) string {
 }
 
 // stripCodeFences removes leading/trailing markdown code fences from LLM output.
+// extractResolvedFileContent pulls the resolved file out of an LLM response.
+// Conflict-resolution models sometimes wrap the file in a ```fenced block with
+// conversational preamble/postamble ("Resolved. Kept X ... File content to
+// apply: ```json {…}``` Grant write to apply."). Writing that whole reply
+// verbatim corrupts the file (it broke a real build's package.json into invalid
+// JSON). When a fenced block is present return ONLY its contents; otherwise
+// fall back to trimming stray fences.
+func extractResolvedFileContent(resp string) string {
+	if i := strings.Index(resp, "```"); i >= 0 {
+		rest := resp[i+3:]
+		if nl := strings.IndexByte(rest, '\n'); nl >= 0 {
+			rest = rest[nl+1:]
+		}
+		if j := strings.Index(rest, "```"); j >= 0 {
+			return strings.TrimSpace(rest[:j])
+		}
+	}
+	return strings.TrimSpace(stripCodeFences(resp))
+}
+
 func stripCodeFences(s string) string {
 	s = strings.TrimSpace(s)
 	if strings.HasPrefix(s, "```") {