The apps subsystem previously sent Cache-Control: public, max-age=300|3600,
must-revalidate but no ETag. With must-revalidate and no validator, the
browser cannot return 304 — it has to refetch the full body once max-age
expires. For mdedit that's 920 KB on every reload after an hour.
Add a content-addressed ETag (sha256 hex prefix, 32 chars) to:
- apps/handler.go's serveBody + serveEmbedded (both paths now emit ETag
+ handle If-None-Match short-circuit to 304)
- handler/directory.go's embedded:browse fallback (mirror behavior so
the bare-directory landing serves the same way)
Drop max-age to 0 with must-revalidate: every page load revalidates,
but a matching ETag returns 304 with empty body. Steady-state cost of
a reload drops from N KB to a few hundred bytes. When the binary is
redeployed, the ETag changes (content hash) and the next request
returns 200 with the new bytes.
Tests in apps/handler_test.go cover both paths:
- TestServer_Embedded_ConditionalGET: full GET, matching INM, stale INM
- TestEmbeddedETag_Stable: same bytes → same ETag, different → different
Live smoke (curl against zddc-server -root /tmp/empty):
GET / → 200, ETag set, body = 80919 bytes (landing.html)
GET / + INM:tag → 304 Not Modified, empty body
ZDDC
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