Gadfly: agentic adversarial PR reviewer (initial extraction)

Standalone, Docker-packaged extraction of the agentic PR reviewer that runs in
Gitea Actions: reads the checked-out repo with read-only tools (read_file/grep/
find_files/get_diff), verifies findings before reporting, two-pass review +
adversarial recheck, posts one labeled comment per model. Advisory only.

- cmd/gadfly: reviewer binary (majordomo + Ollama Cloud), zero deps beyond stdlib + majordomo
- entrypoint.sh: container brains — trigger gating, PR clone, model loop (logic out of YAML)
- Dockerfile: multi-stage; build-time module token never reaches the final image
- .gitea/workflows/build-image.yml: tag v* → build & push image
- examples/: ~15-line consumer stub
- system prompt genericized + hardened to re-derive constants/formulas (semantic bugs)

Vibe-coded with Claude Code; see README disclosure. Advisory, never blocks merge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,30 @@
+# syntax=docker/dockerfile:1
+#
+# Multi-stage so the private-module access token used to fetch the majordomo
+# dependency lives ONLY in the build stage and never lands in the final image.
+
+FROM golang:1.26 AS build
+ARG GIT_HOST=gitea.stevedudenhoeffer.com
+ARG GIT_USER=
+ARG GIT_TOKEN=
+ENV CGO_ENABLED=0 \
+    GOFLAGS=-mod=mod \
+    GOSUMDB=off
+ENV GOPRIVATE=${GIT_HOST}/* GONOSUMDB=${GIT_HOST}/*
+WORKDIR /src
+# Private Go module access (majordomo). Token is confined to this stage.
+RUN if [ -n "$GIT_TOKEN" ]; then \
+      git config --global url."https://${GIT_USER}:${GIT_TOKEN}@${GIT_HOST}/".insteadOf "https://${GIT_HOST}/"; \
+    fi
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN go build -trimpath -ldflags="-s -w" -o /out/gadfly ./cmd/gadfly
+
+FROM alpine:3.20
+RUN apk add --no-cache bash git curl jq ca-certificates
+COPY --from=build /out/gadfly /usr/local/bin/gadfly
+COPY scripts /app/scripts
+COPY entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh /app/scripts/run.sh /usr/local/bin/gadfly
+ENTRYPOINT ["/entrypoint.sh"]