Share one fetch and transcode among concurrent misses (closes #65)

Requests that missed the same variant at once each fetched and
transcoded it. They now share one call through
golang.org/x/sync/singleflight, keyed on the variant cache key. The
first request processes the variant with a context that does not end
with its own; the others wait for its result, holding no connection or
processing slot, and return as soon as their own context ends. The
processing request waits even then, as before. Each request counts one
miss; the processing counts its fetch and transcode once. A panic
while processing becomes an error instead of stopping pixad.

Model: opus-5-5

.dockerignore

@@ -1,8 +1,4 @@
-# .git is sent without its config. Without a VERSION build argument the
-# stage that compiles runs `git describe --tags --always` on .git, which
-# does not need .git/config; that file can hold a credential, such as a
-# password in a remote URL or the token the CI checkout step stores there.
-.git/config
+.git
 .gitignore
 .DS_Store
 .env*

CONVENTIONS.md

@@ -112,13 +112,15 @@ import (
 )
 
 var (
-    Appname string = "CHANGEME"
-    Version string
+    Appname   string = "CHANGEME"
+    Version   string
+    Buildarch string
 )
 
 func main() {
     globals.Appname = Appname
     globals.Version = Version
+    globals.Buildarch = Buildarch
 
     fx.New(
         fx.Provide(
@@ -857,7 +859,7 @@ func (l *Logger) Identify() {
     l.log.Info("starting",
         "appname", l.params.Globals.Appname,
         "version", l.params.Globals.Version,
-        "arch", runtime.GOARCH,
+        "buildarch", l.params.Globals.Buildarch,
     )
 }
 ```
@@ -977,20 +979,23 @@ import "go.uber.org/fx"
 
 // Package-level variables (set from main)
 var (
-    Appname string
-    Version string
+    Appname   string
+    Version   string
+    Buildarch string
 )
 
 // Struct for DI
 type Globals struct {
-    Appname string
-    Version string
+    Appname   string
+    Version   string
+    Buildarch string
 }
 
 func New(lc fx.Lifecycle) (*Globals, error) {
     n := &Globals{
-        Appname: Appname,
-        Version: Version,
+        Appname:   Appname,
+        Buildarch: Buildarch,
+        Version:   Version,
     }
     return n, nil
 }
@@ -1001,13 +1006,15 @@ func New(lc fx.Lifecycle) (*Globals, error) {
 ```go
 // cmd/httpd/main.go
 var (
-    Appname string = "CHANGEME"  // Default, overridden by build
-    Version string               // Set at build time
+    Appname   string = "CHANGEME"  // Default, overridden by build
+    Version   string               // Set at build time
+    Buildarch string               // Set at build time
 )
 
 func main() {
     globals.Appname = Appname
     globals.Version = Version
+    globals.Buildarch = Buildarch
     // ...
 }
 ```
@@ -1018,9 +1025,10 @@ Use ldflags to inject version information at build time:
 
 ```makefile
 VERSION := $(shell git describe --tags --always)
+BUILDARCH := $(shell go env GOARCH)
 
 build:
-    go build -ldflags "-X main.Version=$(VERSION)" ./cmd/httpd
+    go build -ldflags "-X main.Version=$(VERSION) -X main.Buildarch=$(BUILDARCH)" ./cmd/httpd
 ```
 
 ---

Dockerfile

@@ -43,24 +43,13 @@ COPY . .
 RUN make test
 
 # VERSION is declared here, not earlier: a new value reruns only the
-# build, not script/bootstrap or the tests. Given none, the version is
-# `git describe --tags --always` of the .git in the build context (git
-# comes from script/bootstrap): the tag on a tagged commit, tag-N-gHASH
-# after one, the short commit when no tag is reachable. A context that
-# carries .git and still yields no version fails the build; one without
-# .git, as from a source tarball, stamps an empty version. CGO stays
-# enabled for govips; -trimpath keeps build paths out of the binary, and
-# -s -w leave out the symbol table and debug information.
-ARG VERSION
-RUN version="${VERSION:-$(git describe --tags --always)}"; \
-    if [ -e .git ] && { [ -z "$version" ] || [ "$version" = dev ] || \
-        [ "$version" = unknown ]; }; then \
-        echo "the build context carries .git but yields no version" >&2; \
-        exit 1; \
-    fi; \
-    CGO_ENABLED=1 GOTOOLCHAIN=auto go build -trimpath \
-        -ldflags "-s -w -X main.Version=${version}" \
-        -o /pixad ./cmd/pixad
+# build, not script/bootstrap or the tests. CGO stays enabled for
+# govips; -trimpath keeps build paths out of the binary, and -s -w
+# leave out the symbol table and debug information.
+ARG VERSION=dev
+RUN CGO_ENABLED=1 GOTOOLCHAIN=auto go build -trimpath \
+    -ldflags "-s -w -X main.Version=${VERSION}" \
+    -o /pixad ./cmd/pixad
 
 # Runtime stage
 # alpine:3.21, 2026-02-25

TODO.md

@@ -40,13 +40,6 @@ P2: security: referer blacklist
   nothing; each request counts one miss, and the processing counts its fetch
   and transcode once; a panic while processing becomes an error for every
   waiting request instead of stopping pixad; documented in `README.md`.
-- 2026-10-02 a plain `docker build .` stamps the tag or short commit, not
-  `dev` (closes #166): `.dockerignore` lets `.git` into the build context,
-  without `.git/config`; with no `VERSION` build argument the `Dockerfile`
-  takes the version from `git describe --tags --always`, and fails the build if
-  the context carries `.git` and no version comes out; `ARG VERSION` has no
-  default; pixad logs its version, with its name and architecture, as its first
-  log line at startup.
 - 2026-09-29 the container makes `/var/lib/pixa` usable by itself (closes
   #159): `deploy/docker-entrypoint.sh` creates the directory if it is missing,
   gives the directory and everything in it to `pixad` when the directory or one

cmd/pixad/main.go

@@ -56,9 +56,6 @@ func run(_ *cobra.Command, _ []string) {
 			middleware.New,
 			healthcheck.New,
 		),
-		fx.Invoke(
-			func(log *logger.Logger) { log.Identify() },
-			func(*server.Server) {},
-		),
+		fx.Invoke(func(*server.Server) {}),
 	).Run()
 }