--verify keeps a mismatched original until a matching copy replaces it (closes #199)

With --verify, an original whose hash does not match is no longer removed
before its replacement is downloaded. replaceOriginal, beside placeOriginal
in src/library/content.ts, has the content cache's new fetchOriginal write
the replacement to a temporary file beside the original, hashes it, and
renames it over the original only when it matches; a live photo's image and
video are both hashed before either is renamed. A failed or mismatching
download leaves the old bytes and album links, removes the temporary files,
and lands in failures.json. The replacement is always downloaded, never
copied from the cache. The leftover-file cleanup also takes a live photo's
replacement files, .quak-<pid>-<random>.<ext>.

Model: opus-5-5

TODO.md

@@ -17,8 +17,7 @@ pre-1.0
 
 # Next Step
 
-Three bugs are open: https://git.eeqj.de/sneak/quak/issues/198,
-https://git.eeqj.de/sneak/quak/issues/199 and
+Two bugs are open: https://git.eeqj.de/sneak/quak/issues/198 and
 https://git.eeqj.de/sneak/quak/issues/205. The check of quak against a live Ente
 account, https://git.eeqj.de/sneak/quak/issues/187, needs an account only sneak
 has, so it waits on him.
@@ -28,6 +27,16 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-16: With `--verify`, an original whose hash does not match is no
+  longer removed before its replacement is downloaded (issue 199).
+  `replaceOriginal` in `src/library/content.ts` downloads the replacement to a
+  temporary file beside it, a live photo's image and video each to its own,
+  hashes it and renames it over the original only when it matches. When the
+  download fails or does not match either, the original keeps its bytes and
+  links, and the file goes into `failures.json`. The replacement is always
+  downloaded, through the new `fetchOriginal` of the content cache, never copied
+  from the cache.
+
 - 2026-10-16: The `~/bin/quak` that `make install` builds retries a refused
   connection and a name that does not resolve, and the backup records either as
   transient (issue 206). Bun's `fetch` reports them with codes of its own,