feat: bundle handoff-watchdog Claude Code hooks as SDK installer assets

[Gradata]

Problem

Issue #127 landed the context-pressure handoff watchdog as:

• SDK library code in Gradata/src/gradata/contrib/patterns/handoff.py (HandoffWatchdog, HandoffDoc, pick_latest_unconsumed, consume_handoff)
• Claude Code runtime wiring in two JS hooks: .claude/hooks/user-prompt/handoff-watchdog.js + .claude/hooks/session-start/handoff-inject.js (commits f02fde5a + 89cd7fae)

The JS hooks are tracked in this repo via a .gitignore carve-out, but that only helps fresh clones of this repo on this machine. A user on a different machine who does pip install gradata gets the Python pattern but not the Claude Code wiring — the watchdog stays dormant because nothing in their .claude/hooks/ calls HandoffWatchdog.check() or reads the bridge file.

Proposed behavior

Extend Gradata/src/gradata/hooks/_installer.py so it can install Claude-Code-specific JS hooks alongside the existing Python hooks:

1. Ship the JS hooks as package data. Move (or duplicate) handoff-watchdog.js and handoff-inject.js into Gradata/src/gradata/hooks/assets/claude_code/ and include them in pyproject.toml [tool.setuptools.package-data].
2. Installer copy step. Add a function in _installer.py that, when the target project has a .claude/hooks/ directory, copies the JS assets into the correct subdirs (user-prompt/, session-start/). Preserve executable bit.
3. Settings registration. The two hooks need to fire as UserPromptSubmit and SessionStart entries in ~/.claude/settings.json. Since settings.json is already owned by _installer.generate_settings(), add new HOOK_REGISTRY-style entries for the JS hooks (probably a new type=js_asset variant, since the current registry only handles Python modules).
4. CLI entrypoint. gradata install-hooks --include-watchdog (or enabled by default at STANDARD profile) triggers the copy + settings update.
5. Idempotent. Re-running the installer should not duplicate hook entries or clobber user edits — diff against the existing file first.

Out of scope

• Rewriting the JS hooks in Python (they intentionally read Claude Code's statusline bridge file, which is a JS/Node runtime thing)
• Cross-provider support (only Claude Code has the hook surface today; Cursor/Windsurf equivalents are a separate issue)

Acceptance

• JS hook files live under Gradata/src/gradata/hooks/assets/claude_code/ and are included as package data
• _installer.py has a install_js_hooks(project_dir) function (or similar) that copies them into .claude/hooks/ when invoked
• HOOK_REGISTRY extended to include the two JS hooks at the appropriate profile tier
• gradata install-hooks (or existing install command) copies both files and registers them in settings.json
• Unit tests for the copy step (tmp_path fixture, assert files land in correct subdirs with correct content)
• Integration test: run installer against a fresh .claude/, invoke the watchdog by simulating a bridge file, confirm the hook emits the expected directive
• Docs: README section on "Enable context-pressure handoff" with the env var (GRADATA_HANDOFF_THRESHOLD) and a note that the hooks require Claude Code (not provider-agnostic yet)

References

• feat: context-pressure handoff watchdog (preemptive compaction) #127 — the watchdog itself (closed)
• Claude Code integration comment on feat: context-pressure handoff watchdog (preemptive compaction) #127: feat: context-pressure handoff watchdog (preemptive compaction) #127 (comment)
• Hook files at f02fde5a (Sprites Work branch feat/token-optimization-autoresearch)