feat: add volume-mounts and docker-in-docker support

[okrammer]

• Parse volume-mounts section in opencode-sandbox-config.yaml and write to volume-mounts.txt during ocs-rebuild-container
• Parse docker-in-docker scalar flag; when true, inject the Docker socket as an entry in volume-mounts.txt automatically
• Extend YAML parser in ocs-rebuild-container to handle top-level scalars (key: value) alongside section headers (key:), clearing section context on scalar entries; add cfg_ / post-parse pattern for future scalars
• ocs-start-container reads volume-mounts.txt and builds -v flags for each entry; expands env vars in host paths (e.g. $HOME); prints mount summary
• entrypoint.sh: dynamically match docker group GID of mounted socket so dev user can access it regardless of host runtime (Colima, Podman, etc.)
• Add volume-mounts and docker-in-docker entries to init-templates config
• Add docker-cli to mise.toml for this repo's own sandbox
• docs: add Docker-in-Docker setup section to README with mise.toml example
• docs: update AGENTS.md to reflect docker CLI availability and clarify podman/ocs-* constraints

[Copilot]

Pull request overview

Adds support for two new opencode-sandbox-config.yaml features: arbitrary volume-mounts (extra host-to-container bind mounts) and a docker-in-docker flag that mounts the host Docker socket and dynamically aligns the dev user's group membership at container entry. Extends the bash YAML parser in ocs-rebuild-container with a top-level scalar form (key: value), wires the new mounts into ocs-start-container's docker run invocation, and updates the templates, this project's own sandbox config/mise toolchain, and the docs.

Changes:

• Parser change in ocs-rebuild-container to recognize top-level scalars alongside section headers, plus emission of volume-mounts.txt and conditional injection of the docker socket mount.
• ocs-start-container now reads volume-mounts.txt, expands env vars in host paths via eval echo, builds -v flags, and logs them; entrypoint.sh aligns a docker group to the mounted socket's GID and adds the dev user to it.
• Template, sample config, mise.toml, README, and AGENTS.md updates documenting the new feature.

Reviewed changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
bin/ocs-rebuild-container	Adds scalar-vs-section parsing branch, volume-mounts.txt output, and post-parse docker-socket injection.
bin/ocs-start-container	Reads volume-mounts.txt, expands env vars with eval, builds -v flags, logs them, and passes them to docker run.
entrypoint.sh	Creates a docker group matching the mounted socket's GID and adds dev to it.
opencode-sandbox-config.yaml	Enables docker-in-docker: true for this repo's own sandbox; adds placeholder volume-mounts and an unrelated commented host-ports entry.
init-templates/opencode-sandbox-config.yaml	Adds documented volume-mounts and docker-in-docker template entries.
mise.toml	Adds docker-cli for this repo's sandbox.
README.md	Documents volume-mounts, docker-in-docker, and the Docker-in-Docker setup walkthrough.
AGENTS.md	Updates agent-facing notes to reflect docker CLI availability and the scalar-vs-section parser rules.

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[close2infinity]

Reviewed without findings & tested both new features successfully.