#26 Pin Go 1.25 + TinyGo 0.41.1 so the Wasm build compiles

TinyGo 0.41.1's bundled net/http override (roundtrip_js.go) fails to
compile against the Go 1.26 stdlib:

  net/http/roundtrip_js.go:73:12: t.roundTrip undefined (type *Transport
  has no field or method roundTrip, but does have method RoundTrip)

This is tinygo-org/tinygo#5467 (closed 2026-06-20, but not in any tagged
TinyGo release as of 0.41.1, released 2026-04-22). Go 1.25.x is the
newest line TinyGo 0.41.1 fully supports; syumai/workers v0.33.0 needs
only go 1.21.3 and the handler uses only net/http + encoding/json, so
downgrading is safe:

- go.mod: go 1.26.2 -> go 1.25.0 (so GOTOOLCHAIN won't auto-upgrade past
  what TinyGo supports)
- ci.yml: setup-go go-version 1.26 -> 1.25 (TinyGo pin stays 0.41.1)
- README: document the pinned TinyGo/Go matrix and the #5467 rationale

go vet ./..., go test ./..., and actionlint stay green locally.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -33,14 +33,21 @@ jobs:
       - name: Check out repository
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
 
+      # Pinned to Go 1.25 (not 1.26) to match TinyGo. TinyGo 0.41.1's bundled
+      # net/http override (roundtrip_js.go) fails to compile against the Go 1.26
+      # stdlib -- "t.roundTrip undefined ... has method RoundTrip"
+      # (tinygo-org/tinygo#5467, unfixed in any tagged TinyGo release as of
+      # 0.41.1). Go 1.25.x is the newest line TinyGo 0.41.1 fully supports. The
+      # go.mod `go` directive is pinned to 1.25 too, so GOTOOLCHAIN won't
+      # auto-upgrade. go vet/test also run on this version.
       - name: Set up Go
         uses: actions/setup-go@924ae3a1cded613372ab5595356fb5720e22ba16 # v6.5.0
         with:
-          go-version: '1.26'
+          go-version: '1.25'
 
-      # TinyGo is needed only for the Wasm Worker build (pnpm run build). The
-      # 0.41.x line is the first with Go 1.26 support; install-binaryen (default
-      # true) provides wasm-opt, which TinyGo invokes for the -target wasm build.
+      # TinyGo is needed only for the Wasm Worker build (pnpm run build).
+      # install-binaryen (default true) provides wasm-opt, which TinyGo invokes
+      # for the -target wasm build.
       - name: Set up TinyGo
         uses: acifani/setup-tinygo@dd8a7075d951a7595b2ef2123ed0ab1af0c13e56 # v3.0.0
         with:

README.md

@@ -64,7 +64,10 @@ This runs the exact handler the deployed Worker uses, minus the Workers runtime.
 ### Build & run the real Worker (requires TinyGo)
 
 Node tooling is managed with **pnpm**; wrangler is a dev dependency. The Wasm
-build uses [TinyGo](https://tinygo.org) 0.35.0+.
+build uses [TinyGo](https://tinygo.org) 0.41.1 on the Go 1.25.x toolchain.
+(TinyGo 0.41.1 cannot compile `net/http` against Go 1.26 — see
+[tinygo-org/tinygo#5467](https://github.com/tinygo-org/tinygo/issues/5467) —
+so the module pins `go 1.25` in `go.mod`; CI installs and enforces this.)
 
 ```console
 pnpm install                 # install wrangler

go.mod

@@ -1,5 +1,5 @@
 module github.com/JMR-dev/LibreMail-Bug-Report-Ingest
 
-go 1.26.2
+go 1.25.0
 
 require github.com/syumai/workers v0.33.0