[myieye]

[Claude, autonomous]

A user opening a large changeset diff in hgweb blew the pod's memory. hgweb keeps a file's whole diff in memory while rendering and diffs the changeset twice (diffstat), and Mercurial has no cap for this. The new diffguard extension sizes the files a page would diff from the revlog index; over diffguard.maxbytes (32 MB before+after) the changeset page is served without the diff (file list and per-file links still work) and the single-file diff/comparison/annotate pages answer 403.

• Measured on the published image: a 26 MB file rewrite peaked at ~320 MB RSS and a 45 MB rewrite got the mod_wsgi daemon OOM-killed in a 600 MiB cgroup; with the guard both pages return in under a second.
• Peak RSS is roughly 6-8x the bytes touched, so 32 MB caps a request at ~250 MB. Tune in hgweb.hgrc ([diffguard] maxbytes, 0 disables).
• Tested with Mercurial 6.3.2 (the image's version) against all hgweb styles, the json-lex log Lexbox uses, removed/added files, bad revisions and missing files; those paths behave as before.
• Deploy order is safe: if the configmap lands before the image, hg logs a failed-extension warning and serves normally.

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