Keep .git/ in the sim image for revision tracking

[YWHyuk]

Summary

Currently the sim image only carries a single /workspace/.git-rev line because the builder stage runs find -name .git -prune -exec rm -rf {} +. That's enough to identify a tag but not to do real debugging: no git log for context, no git submodule status for submodule SHAs (chakra, ns-3, etc.), no git diff for hotfix verification.

This patch keeps .git/ (main repo + recursive submodules), installs git in the runtime stage, and runs git gc --aggressive --prune=now everywhere to compact packs.

Changes

• scripts/sim.Dockerfile builder stage: replace the .git wipe with git gc --aggressive --prune=now on the main repo plus git submodule foreach --recursive 'git gc --aggressive --prune=now' so submodule .git/modules/<name>/ packs (the bulk of the footprint) get compacted too. The submodule foreach is wrapped in a subshell + || true so a single submodule failure doesn't abort the build, scoped so the rest of the && chain still aborts on real errors.
• Runtime stage: install git, add git config --system --add safe.directory '*' (root-owned .git tree may now be inspected by enroot --user / docker -u UIDs).
• Update Dockerfile header comment + .dockerignore comment to document the new contract.

After this lands

docker run --rm <image> bash -lc 'cd /workspace && git log -3 --oneline'
docker run --rm <image> bash -lc 'cd /workspace && git submodule status --recursive'
docker run --rm <image> cat /workspace/.git-rev

Size impact (measured)

Smoke test on a full dev clone of this repo (deep history; CI runs are shallower):

	.git/ total
Before gc	305 MB
After gc	210 MB (~31% reduction)

The root .git/ shrinks ~1 MB because it's already packed; the real win is on .git/modules/* (278 MB of submodule packs in this dev clone -> ~180 MB after submodule foreach gc).

CI shallow checkouts (actions/checkout with default fetch-depth: 1 + submodules: recursive) start much smaller, so the runtime image overhead from published builds will be well below 210 MB.

Interaction with #39

Both PRs touch scripts/sim.Dockerfile. #39 adds ARG GIT_SHA + an OCI label for fast version inspection without running the container; this PR adds the full .git/ tree for deep debugging. They're complementary, but whichever merges second will need a tiny rebase (the header comment block and the same RUN step). No semantic conflict.

Test plan

• PR build succeeds on linux/amd64 and linux/arm64.
• After merge: docker run --rm ghcr.io/psal-postech/llmservingsimspec/sim:latest cat /workspace/.git-rev returns the merge commit SHA.
• After merge: docker run --rm <image> bash -lc 'cd /workspace && git log -1 --format=%H' matches that SHA.
• After merge: docker run --rm <image> bash -lc 'cd /workspace && git submodule status --recursive' lists every submodule with its SHA -- including astra-sim and the sub-submodules under astra-sim/extern/.
• After merge: docker image inspect <image> --format '{{.Size}}' is within ~250 MB of the previous published image size (sanity check on .git bloat).

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