bug: git tags and env vars not injected into docker build when using --build flag

[bnema]

Summary

gordon push --build only injects VERSION as a build arg, using the bare-name form (--build-arg VERSION). Many project Dockerfiles use different variable names (GIT_TAG, GIT_SHA, BUILD_TIME) that Gordon never populates automatically. The make push approach works because Makefiles pass these values explicitly as KEY=VALUE.

Root Cause

File: internal/adapters/in/cli/push.go:467, 490-506

Gordon does two things:

1. Sets VERSION=<resolved> in the subprocess environment
2. Passes --build-arg VERSION (bare name — inherits from subprocess env)

It passes nothing else. A Dockerfile like this (real-world example):

ARG GIT_TAG=unknown
ARG GIT_SHA=unknown
ARG BUILD_TIME=unknown
ENV PUBLIC_APP_VERSION=${GIT_TAG}

…gets GIT_TAG=unknown because Gordon never injects it. The app binary reports "unknown" at runtime.

Why make push Works

A typical Makefile pre-computes all git values and passes them explicitly as KEY=VALUE:

docker buildx build \
  --build-arg GIT_TAG=$(shell git describe --tags --abbrev=0) \
  --build-arg GIT_SHA=$(shell git rev-parse --short HEAD) \
  --build-arg BUILD_TIME=$(shell date -u +%Y-%m-%dT%H:%M:%SZ) \
  --build-arg VERSION=$(VERSION) \
  ...

KEY=VALUE form is also more reliable than bare KEY — it does not depend on env inheritance behaviour across Docker daemon versions.

Proposed Fix

Gordon should automatically inject the following standard git build args into every --build invocation, as explicit KEY=VALUE pairs:

Build arg	Source	Example
VERSION	git describe / CI env / --tag flag	v1.2.3
GIT_TAG	same as VERSION	v1.2.3
GIT_SHA	git rev-parse --short HEAD	abc1234
BUILD_TIME	time.Now().UTC().Format(time.RFC3339)	2026-02-24T10:00:00Z

These should be passed as --build-arg GIT_TAG=v1.2.3 (not bare name), matching the convention used by typical Makefiles. The user-supplied --build-arg flags (via CLI) still take precedence and are appended after, so they can override any of these defaults.

Additional: silent fallback to "latest"

File: internal/adapters/in/cli/push.go:685

func getGitVersion(ctx context.Context) string {
    out, err := exec.CommandContext(ctx, "git", "describe", "--tags", "--dirty").Output()
    if err != nil {
        return ""  // silently becomes "latest", no log
    }
    return strings.TrimSpace(string(out))
}

When a repo has no git tags, version silently falls back to "latest" with no warning. A log message should be emitted so the user understands why their image has no version tag.

Affected Files

• internal/adapters/in/cli/push.go:467 — subprocess env setup
• internal/adapters/in/cli/push.go:490 — buildImageArgs() — where --build-arg flags are assembled
• internal/adapters/in/cli/push.go:685 — getGitVersion() — silent fallback