fix(sync): force host static-config stages user-writable (read-only source → EACCES)

[afterthought]

Problem

agentbox prepare (and the docker/cloud seeds) fail for anyone whose agent config is managed declaratively — Nix/home-manager, Ansible, chezmoi, or just root-owned/read-only dotfiles:

prepare failed: EACCES: permission denied, unlink
  '/var/folders/.../agentbox-claude-static-stage-wV1H1q/skills/1password/SKILL.md'

Root cause

The static-config stages (stage{Claude,Codex,Agents,Opencode}StaticForUpload in packages/sandbox-core/src/sync/host-stage.ts) rsync ~/.claude, ~/.codex, ~/.agents, and ~/.local/share/opencode into a throwaway scratch dir, then rewrite it in place (filter settings.json, sanitize config.toml, rewrite plugin paths) and finally rm it.

Every one of those rsyncs runs rsync -a, which implies -p and preserves the source's modes. When the source is read-only — skill/plugin symlinks into the Nix store (0444/0555), or any root-owned / 0444 dotfile — the scratch copy is read-only too. That breaks the stage two ways:

1. the in-place writeFile rewrites fail with EACCES; and
2. cleanup's rm can't unlink a child of a 0555 directory → the unlink .../skills/*/SKILL.md above.

A normal writable ~/.claude never hits it, which is why it only bites declaratively-managed hosts.

Fix

A scratch dir has no business inheriting the source's perms. Add --chmod=Du+rwx,Fu+rw (via a shared, documented STAGE_WRITABLE_CHMOD constant) to each of the 5 stage rsyncs. GNU rsync honors it; macOS's openrsync ignores it and doesn't hit the read-only-source case in practice, so it's a safe no-op there.

Scoped to the static-config stages only — the workspace export rsync is untouched, so its -i itemized output (parsed by parseItemizedChanges) is unchanged.

Reproduce

On a host where ~/.claude/skills/* are read-only symlinks into a read-only store (e.g. home-manager), or synthetically:

mkdir -p /tmp/ro/skills/x && echo hi > /tmp/ro/skills/x/SKILL.md
chmod -R a-w /tmp/ro/skills
rsync -a /tmp/ro/ /tmp/stage/ && rm -rf /tmp/stage   # EACCES on the rm
rsync -a --chmod=Du+rwx,Fu+rw /tmp/ro/ /tmp/stage2/ && rm -rf /tmp/stage2   # clean

🤖 Generated with Claude Code

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
agentbox-web	Skipped		Jul 8, 2026 4:36pm

[madarco]

thanks for the PR