Decompose muse/cli/commands/bridge.py (3138 lines) into focused modules

Summary

`muse/cli/commands/bridge.py` is 3138 lines and owns eight distinct responsibilities. Like `store.py` before it, it is a god object — every bridge operation (import, export, status, hooks, state I/O, git subprocess wrappers, harmony/shelf migration, drift computation) runs through it. This issue tracks a phased decomposition into focused, single-responsibility modules.

Goal: zero functional change, zero test regressions, cleaner architecture.

The destination is a `muse/core/bridge/` package that owns all domain logic, with `muse/cli/commands/bridge.py` reduced to a thin argparse registration shell (≤ 200 lines).

Responsibility map (current)

Target layout

``` muse/core/bridge/ init.py — re-exports public API (BridgeState, run_git_import, …) state.py — TOML state types + read/write hooks.py — hook loading and dispatch git_primitives.py — subprocess wrappers (git, _CatFile, _batch*, …) importer.py — Git → Muse import engine harmony_shelf.py — rerere↔harmony and stash↔shelf migration exporter.py — Muse → Git export engine + watch loop status.py — drift computation and status formatting muse/cli/commands/bridge.py — thin shell: argparse registration only (≤ 200 lines) ```

Phase 1 — Create `muse/core/bridge/state.py`

Scope: TOML state types and persistence.

Extract:

• `_LastImportState`, `_LastExportState`, `BridgeState`, `_SidecarData`, `DriftInfo` (TypedDicts / dataclasses)
• `read_bridge_state`, `write_bridge_state`, `_dict_to_toml`

Acceptance: `muse/core/bridge/state.py` exists, all callers in `bridge.py` updated to import from it, all bridge tests pass.

Phase 2 — Create `muse/core/bridge/hooks.py`

Scope: lifecycle hook loading and dispatch.

Extract:

• `BridgeHook`, `BridgeHooks` (TypedDicts)
• `load_bridge_hooks`, `run_hook`, `run_hooks`

Acceptance: hook logic fully decoupled from import/export engines, all bridge tests pass.

Phase 3 — Create `muse/core/bridge/git_primitives.py`

Scope: low-level git subprocess I/O. No Muse domain knowledge.

Extract:

• `AttributionMapper` — author/committer → Muse identity mapping
• `_CatFile` — git cat-file --batch process wrapper
• `_git` — subprocess runner
• `_batch_commit_log` — bulk commit log reader
• `_batch_diff_tree` — bulk diff-tree reader
• `_is_lfs_pointer`, `_strip_ansi`, `_parse_sem_ver_bump`

Acceptance: no git subprocess logic remains in `bridge.py`, all bridge tests pass.

Phase 4 — Create `muse/core/bridge/importer.py`

Scope: Git → Muse commit replay engine.

Extract:

• `_replay_commit` (~140 lines)
• `_replay_branch` (~188 lines)
• `_list_git_branches`, `_list_git_tags`, `_import_tags`
• `run_git_import` (~213 lines)

Internal dependencies: imports from `git_primitives`, `state`, `hooks`.

Acceptance: `run_git_import` callable from `muse.core.bridge.importer`, no import logic in `bridge.py`, `test_bridge_git_import.py` fully green.

Phase 5 — Create `muse/core/bridge/harmony_shelf.py`

Scope: cross-system data migration (rerere ↔ harmony, stash ↔ shelf).

Extract:

• `import_rerere_to_harmony` (~136 lines)
• `export_harmony_to_rerere` (~63 lines)
• `import_stashes_to_shelf` (~135 lines)
• `export_shelves_to_stash` (~112 lines)

Acceptance: migration logic isolated, `test_bridge_harmony_shelf.py` fully green.

Phase 6 — Create `muse/core/bridge/exporter.py`

Scope: Muse → Git export engine and watch loop.

Extract:

• `_validate_git_sha`, `_validate_git_branch_name`
• `GitExporter` class (~360 lines)
• `_ensure_git_branch`, `_watch_loop`
• `run_git_export` (~188 lines)

Internal dependencies: imports from `git_primitives`, `state`, `hooks`.

Acceptance: `run_git_export` callable from `muse.core.bridge.exporter`, `test_bridge_git_export.py` and `test_bridge_watch.py` fully green.

Phase 7 — Create `muse/core/bridge/status.py`

Scope: drift computation and status display.

Extract:

• `run_git_status`
• `_compute_drift`, `_count_muse_commits_since`
• `_print_bridge_status_text`

Acceptance: `test_bridge_git_status.py` fully green.

Phase 8 — Create `muse/core/bridge/init.py`, thin the CLI shell, delete dead code

Scope: final wiring and cleanup.

• Create `muse/core/bridge/init.py` exporting the public API
• Reduce `muse/cli/commands/bridge.py` to argparse registration only (≤ 200 lines: `register`, `_register_git_import`, `_register_git_export`, `_register_git_status`)
• Run `muse code dead --high-confidence-only` and delete anything unreachable
• Update any doc references to `muse/cli/commands/bridge.py` internals
• Update `test_bridge_phase1.py` and `test_bridge_security.py` if they reference internal paths

Acceptance:

• `muse/cli/commands/bridge.py` ≤ 200 lines, contains only argparse wiring
• `muse code breakage` — 0 issues
• `muse code test` — clean
• All `test_bridge_*.py` files pass
• No stale doc references

Cross-cutting rules (all phases)

• No functional changes in any phase — pure mechanical extraction
• Each phase is its own commit on a task branch
• Each phase merges independently to dev before the next starts
• No backward-compat shims, no re-exports, no deprecated annotations
• Delete everything that is unused after extraction
• `muse code test --json` must pass before each phase merges
• Circular import guard: `git_primitives` has no knowledge of Muse domain types; `importer`/`exporter` import from `git_primitives` and `state` but never from each other

Test files to keep green throughout

• `tests/test_bridge_git_import.py`
• `tests/test_bridge_git_export.py`
• `tests/test_bridge_git_status.py`
• `tests/test_bridge_hooks.py`
• `tests/test_bridge_harmony_shelf.py`
• `tests/test_bridge_watch.py`
• `tests/test_bridge_roundtrip.py`
• `tests/test_bridge_phase1.py`
• `tests/test_bridge_security.py`