build(#283): uv best-practice polish (cache mounts, .python-version, drop redundant PYTHONPATH)

Follow-up tidy from a best-practices review of the uv adoption:
- Dockerfile: swap UV_NO_CACHE for BuildKit cache mounts on the `uv sync`
  steps (the documented uv-in-Docker pattern) — faster rebuilds, and the
  cache stays out of the image layers.
- Add build/dashboard/.python-version (3.11) so local `uv` defaults to the
  same interpreter as the digest-pinned Docker base and CI.
- Drop the now-redundant PYTHONPATH=build/dashboard from the fakes test
  (Makefile + CI): uv editable-installs the project into the venv, so the
  source no longer needs to be on sys.path. Verified the fakes still pass (12).

Re-verified: docker test stage (532 tests in-container) + prod stage build
with cache mounts; make test-dashboard/test-fakes/lint-py green; uv lock --check clean.

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

Author: VijitSingh97

.github/workflows/ci.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Fake-daemon contract test (real clients vs controllable fakes)
         # Points the real Monero/Tari clients at the integration fakes and asserts they parse
         # every state (synced/syncing/down). Docker-free, so it runs on every PR (issue #54).
-        run: PYTHONPATH=build/dashboard uv run --locked --project build/dashboard --extra test python -m pytest tests/integration/fakes -q
+        run: uv run --locked --project build/dashboard --extra test python -m pytest tests/integration/fakes -q
 
   frontend:
     name: Frontend logic tests (node --test)

Makefile

@@ -17,8 +17,7 @@ test-integration-selftest: ## Integration harness pure-logic self-test (no serve
 	bash tests/integration/selftest.sh
 
 test-fakes: ## Fake-daemon contract test — real dashboard clients vs controllable fakes (no docker)
-	PYTHONPATH=build/dashboard uv run --locked --project build/dashboard --extra test \
-		python -m pytest tests/integration/fakes -q
+	uv run --locked --project build/dashboard --extra test python -m pytest tests/integration/fakes -q
 
 test-mini-stack: ## Fake-daemon docker mini-stack end-to-end (needs docker; CI)
 	bash tests/integration/mini-stack/run-mini-stack.sh

build/dashboard/.python-version

@@ -0,0 +1 @@
+3.11

build/dashboard/Dockerfile

@@ -10,12 +10,11 @@ COPY --from=ghcr.io/astral-sh/uv:0.10.10@sha256:cbe0a44ba994e327b8fe7ed72beef1aa
 
 # Install into a project venv on PATH (so entrypoint.sh's `python3` resolves to it); use the
 # digest-pinned base interpreter (never let uv download a different Python); compile bytecode and
-# copy (not hardlink) since the cache and target may be on different layers.
+# copy (not hardlink) from the BuildKit cache mount used on the sync steps below.
 ENV UV_PYTHON_DOWNLOADS=never \
     UV_PROJECT_ENVIRONMENT=/app/.venv \
     UV_COMPILE_BYTECODE=1 \
     UV_LINK_MODE=copy \
-    UV_NO_CACHE=1 \
     PATH="/app/.venv/bin:$PATH"
 
 # System dependencies.
@@ -36,7 +35,7 @@ COPY mining_dashboard/ ./mining_dashboard/
 # a normal `docker compose build` targets the production stage and skips it.
 # ==========================================================================
 FROM base AS test
-RUN uv sync --locked --extra test
+RUN --mount=type=cache,target=/root/.cache/uv uv sync --locked --extra test
 COPY tests/ ./tests/
 RUN python -m pytest --cov=mining_dashboard --cov-report=term-missing --cov-fail-under=80
 
@@ -45,7 +44,7 @@ RUN python -m pytest --cov=mining_dashboard --cov-report=term-missing --cov-fail
 # ==========================================================================
 FROM base AS production
 # Runtime deps + the package only (no test/dev extras).
-RUN uv sync --locked
+RUN --mount=type=cache,target=/root/.cache/uv uv sync --locked
 COPY entrypoint.sh .
 RUN chmod +x entrypoint.sh