fix(inbox-send): never overwrite on filename collision

Two sends in the same minute whose text starts with the same phrase derived identical filenames, and the second silently replaced the first. A message was lost this way in the wild. An existing target now gets a -2/-3 stem suffix, extension preserved, on both the text and file paths. Four red-first tests reproduce the loss with a fixed timestamp so the same-minute case is deterministic.

1 files changed, 19 insertions, 2 deletions

diff --git a/.ai/scripts/inbox-send.py b/.ai/scripts/inbox-send.py
index 1362a1f..1ebb636 100755
--- a/.ai/scripts/inbox-send.py
+++ b/.ai/scripts/inbox-send.py
@@ -177,6 +177,23 @@ def build_text_org(message: str, source_name: str, timestamp: str) -> str:
     )
 
 
+def uniquify(dest: Path) -> Path:
+    """Return dest, or dest with a -2/-3/... stem suffix when it already exists.
+
+    Two sends in the same minute whose text starts with the same phrase
+    derive identical filenames, and the second silently overwrote the
+    first (a message was lost this way, 2026-07-02). Never overwrite.
+    """
+    if not dest.exists():
+        return dest
+    n = 2
+    while True:
+        candidate = dest.with_name(f"{dest.stem}-{n}{dest.suffix}")
+        if not candidate.exists():
+            return candidate
+        n += 1
+
+
 def send_text(
     target_inbox: Path,
     message: str,
@@ -191,7 +208,7 @@ def send_text(
     if not slug:
         raise ValueError(f"could not derive a slug from text: {message!r}")
     filename = f"{now.strftime(TS_FILENAME_FMT)}-from-{source_name}-{slug}.org"
-    dest = target_inbox / filename
+    dest = uniquify(target_inbox / filename)
     dest.write_text(build_text_org(message, source_name, now.strftime(TS_DOC_FMT)))
     return dest
 
@@ -211,7 +228,7 @@ def send_file(
         raise ValueError(f"could not derive a slug from file: {src_path}")
     ext = src_path.suffix
     filename = f"{now.strftime(TS_FILENAME_FMT)}-from-{source_name}-{slug}{ext}"
-    dest = target_inbox / filename
+    dest = uniquify(target_inbox / filename)
     shutil.copy2(src_path, dest)
     return dest