Stop the gate stamping VCS metadata into throwaway binaries (#122)

The loop works in a git worktree under the temp directory, and Go's VCS
stamping fails there:

  error obtaining VCS status: exit status 128
  Use -buildvcs=false to disable VCS stamping.

It fails before any repo code compiles, so every agent run reports a red
gate for a reason that has nothing to do with the change under test. A
gate that cannot run where the loop runs is not a gate, and one that fails
for unrelated reasons invites someone to weaken it.

The gate builds binaries it throws away. Stamping git metadata into them
buys nothing and couples the gate to git plumbing it does not need.

Nothing user-visible depends on it. buildinfo reads the module version
from debug.ReadBuildInfo, not the VCS stamp, and release binaries are
built separately in release.yml with the version passed via -ldflags.

Author: charlesgreen

Makefile

@@ -19,11 +19,19 @@ workflows: ## Workflow YAML parses, no conflict markers, no disabled safety cont
 vet: ## go vet across all packages.
 	go vet ./...
 
+# -buildvcs=false: the gate builds throwaway binaries, so stamping git metadata
+# into them buys nothing and couples the gate to git plumbing it does not need.
+# It also breaks the agent loop outright. The loop works in a worktree under the
+# temp directory, and Go's VCS stamping fails there with
+# "error obtaining VCS status: exit status 128", before any repo code compiles.
+# A gate that cannot run where the loop runs is not a gate. Release binaries are
+# built separately in .github/workflows/release.yml and take their version from
+# -ldflags, not from stamping, so nothing user-visible depends on this.
 build: ## Build all packages.
-	go build ./...
+	go build -buildvcs=false ./...
 
 test: ## Run all tests and write a coverage profile for CI upload.
-	go test -race -coverprofile=coverage.txt -covermode=atomic ./...
+	go test -buildvcs=false -race -coverprofile=coverage.txt -covermode=atomic ./...
 
 tidy: ## Tidy the module graph.
 	go mod tidy