docs/architecture/muse-vcs.md · cgcardona/muse

# Muse VCS — Architecture Reference

> **Version:** v0.1.2

> **See also:** [Plugin Authoring Guide](../guide/plugin-authoring-guide.md) · [CRDT Reference](../guide/crdt-reference.md) · [E2E Walkthrough](muse-e2e-demo.md) · [Plugin Protocol](../protocol/muse-protocol.md) · [Domain Concepts](../protocol/muse-domain-concepts.md) · [Type Contracts](../reference/type-contracts.md)

---

## What Muse Is

Muse is a **domain-agnostic version control system for multidimensional state**. It provides

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a complete DAG engine — content-addressed objects, commits, branches, three-way merge, drift

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detection, time-travel checkout, and a full log graph — with one deliberate gap: it does not

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know what "state" is.

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That gap is the plugin slot. A `MuseDomainPlugin` tells Muse how to interpret your domain's

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data. Everything else — the DAG, object store, branching, lineage walking, log, merge state

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machine — is provided by the core engine and shared across all domains.

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Muse v1.0 adds **four layers of semantic richness** on top of that base, each implemented as

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an optional protocol extension that plugins can adopt without breaking anything:

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| Phase | Protocol | What you gain |

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|-------|----------|---------------|

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| 1 — Typed Delta Algebra | `MuseDomainPlugin` (required) | Rich, typed operation lists instead of opaque file diffs |

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| 2 — Domain Schema | `MuseDomainPlugin.schema()` (required) | Algorithm selection driven by declared data structure |

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| 3 — OT Merge Engine | `StructuredMergePlugin` (optional) | Sub-file auto-merge using Operational Transformation |

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| 4 — CRDT Semantics | `CRDTPlugin` (optional) | Convergent join — no conflicts ever possible |

---

## The Seven Invariants

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```

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State = a serializable, content-addressed snapshot of any multidimensional space

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Commit = a named delta from a parent state, recorded in a DAG

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Branch = a divergent line of intent forked from a shared ancestor

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Merge = three-way reconciliation of two divergent state lines against a common base

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Drift = the gap between committed state and live state

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Checkout = deterministic reconstruction of any historical state from the DAG

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Lineage = the causal chain from root to any commit

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```

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None of those definitions contain the word "music."

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## Repository Structure on Disk

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Every Muse repository is a `.muse/` directory:

```

.muse/

repo.json — repository ID, domain name, creation metadata

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HEAD — ref pointer, e.g. refs/heads/main

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config.toml — optional local config (auth token, remotes)

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refs/

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heads/

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main — SHA-256 commit ID of branch HEAD

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feature/… — additional branch HEADs

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objects/

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<sha2>/ — shard directory (first 2 hex chars)

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<sha62> — raw content-addressed blob

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commits/

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<commit_id>.json — CommitRecord (includes structured_delta since Phase 1)

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snapshots/

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<snapshot_id>.json — SnapshotRecord (manifest: {path → object_id})

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tags/

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<tag_id>.json — TagRecord

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MERGE_STATE.json — present only during an active merge conflict

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muse-work/ — the working tree (domain files live here)

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.museattributes — optional: per-path merge strategy overrides (TOML)

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.museignore — optional: snapshot exclusion rules (TOML, domain-scoped)

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```

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The object store mirrors Git's loose-object layout: sharding by the first two hex characters

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of each SHA-256 digest prevents filesystem degradation as the repository grows.

---

## Core Engine Modules

```

muse/

domain.py — all protocol definitions and shared type aliases

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core/

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store.py — file-based commit / snapshot / tag CRUD

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repo.py — repository detection (MUSE_REPO_ROOT or directory walk)

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snapshot.py — content-addressed snapshot and commit ID derivation

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object_store.py — SHA-256 blob storage under .muse/objects/

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merge_engine.py — three-way merge + CRDT join entry points

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op_transform.py — Operational Transformation (Phase 3)

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schema.py — DomainSchema TypedDicts (Phase 2)

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diff_algorithms/ — LCS, tree-edit, numerical, set diff (Phase 2)

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crdts/ — VectorClock, LWWRegister, ORSet, RGA, AWMap, GCounter (Phase 4)

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errors.py — ExitCode enum

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attributes.py — .museattributes loading and strategy resolution

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plugins/

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registry.py — domain name → MuseDomainPlugin instance

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music/

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plugin.py — MidiPlugin: reference implementation of all protocols

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midi_diff.py — note-level MIDI diff and MIDI reconstruction

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scaffold/

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plugin.py — copy-paste template for new domain plugins

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cli/

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app.py — Typer application root, command registration

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commands/ — one file per Tier 2 command; plumbing/ for Tier 1

```

---

## Deterministic ID Derivation

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All IDs are SHA-256 digests — the DAG is fully content-addressed:

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```

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object_id = sha256(raw_file_bytes)

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snapshot_id = sha256(sorted("path:object_id\n" pairs))

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commit_id = sha256(sorted_parent_ids | snapshot_id | message | timestamp_iso)

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```

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The same snapshot always produces the same ID. Two commits that point to identical state share

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a `snapshot_id`. Objects are never overwritten — write is always idempotent.

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## Phase 1 — Typed Delta Algebra

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Every commit now carries a `structured_delta: StructuredDelta` alongside the snapshot

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manifest. A `StructuredDelta` is a list of typed `DomainOp` entries:

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| Op type | Meaning |

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|---------|---------|

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| `InsertOp` | An element was added at a position |

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| `DeleteOp` | An element was removed |

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| `MoveOp` | An element was repositioned |

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| `ReplaceOp` | An element's value changed (before/after content hashes) |

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| `PatchOp` | A container was internally modified (carries child ops recursively) |

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This replaces the old opaque `{added, removed, modified}` path lists entirely. Every operation

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carries a `content_id` (SHA-256 hash of the element), an `address` (domain-specific location),

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and a `content_summary` (human-readable description for `muse show`).

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`muse show <commit>` and `muse diff` display note-level diffs for MIDI files — not just "file

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changed" but "3 notes added at bar 4, 1 note removed from bar 7."

---

## Phase 2 — Domain Schema & Diff Algorithm Library

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Plugins implement `schema() -> DomainSchema` to declare the structural shape of their data.

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The schema drives algorithm selection in `diff_by_schema()`:

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| Schema kind | Diff algorithm | Use when… |

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|-------------|---------------|-----------|

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| `"sequence"` | Myers LCS | Ordered lists (note events, DNA sequences) |

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| `"tree"` | LCS-based tree edit | Hierarchical structures (scene graphs, XML) |

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| `"tensor"` | Epsilon-tolerant numerical | N-dimensional arrays (simulation grids) |

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| `"set"` | Hash-set algebra | Unordered collections (annotation sets) |

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| `"map"` | Per-key comparison | Key-value maps (manifests, configs) |

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`DomainSchema.merge_mode` controls which merge path the core engine takes:

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- `"three_way"` — classic three-way merge (Phases 1–3)

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- `"crdt"` — convergent CRDT join (Phase 4)

---

## Phase 3 — Operation-Level Merge Engine

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Plugins that implement `StructuredMergePlugin` gain sub-file auto-merge:

```python

@runtime_checkable

class StructuredMergePlugin(MuseDomainPlugin, Protocol):

def merge_ops(

self,

base: StateSnapshot,

ours_snap: StateSnapshot,

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theirs_snap: StateSnapshot,

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ours_ops: list[DomainOp],

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theirs_ops: list[DomainOp],

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*,

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repo_root: pathlib.Path | None = None,

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) -> MergeResult: ...

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```

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The core merge engine detects this with `isinstance(plugin, StructuredMergePlugin)` and calls

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`merge_ops()` when both branches have `StructuredDelta`. Non-supporting plugins fall back to

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file-level `merge()` automatically.

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### Operational Transformation (`muse/core/op_transform.py`)

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| Function | Purpose |

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|----------|---------|

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| `ops_commute(a, b)` | Returns `True` when two ops can be applied in either order |

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| `transform(a, b)` | Adjusts positions so the diamond property holds |

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| `merge_op_lists(base, ours, theirs)` | Three-way OT merge; returns `MergeOpsResult` |

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| `merge_structured(base_delta, ours_delta, theirs_delta)` | Wrapper for `StructuredDelta` inputs |

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**Commutativity rules (all 25 op-pair combinations covered):**

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- Different addresses → always commute

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- `InsertOp` + `InsertOp` at same position → conflict

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- `DeleteOp` + `DeleteOp` same content_id → idempotent (not a conflict)

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- `PatchOp` + `PatchOp` → recursive check on child ops

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- Cross-type pairs → generally commute (structural independence)

---

## Phase 4 — CRDT Semantics

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Plugins that implement `CRDTPlugin` replace three-way merge with a mathematical `join` on a

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lattice. **`join` always succeeds — no conflict state ever exists.**

```python

@runtime_checkable

class CRDTPlugin(MuseDomainPlugin, Protocol):

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def crdt_schema(self) -> list[CRDTDimensionSpec]: ...

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def join(self, a: CRDTSnapshotManifest, b: CRDTSnapshotManifest) -> CRDTSnapshotManifest: ...

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def to_crdt_state(self, snapshot: StateSnapshot) -> CRDTSnapshotManifest: ...

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def from_crdt_state(self, crdt: CRDTSnapshotManifest) -> StateSnapshot: ...

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```

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Entry point: `crdt_join_snapshots()` in `merge_engine.py`.

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### CRDT Primitive Library (`muse/core/crdts/`)

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| Primitive | File | Best for |

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|-----------|------|---------|

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| `VectorClock` | `vclock.py` | Causal ordering between agents |

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| `LWWRegister` | `lww_register.py` | Scalar values; last write wins |

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| `ORSet` | `or_set.py` | Unordered sets; adds always win |

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| `RGA` | `rga.py` | Ordered sequences (collaborative editing) |

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| `AWMap` | `aw_map.py` | Key-value maps; adds win |

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| `GCounter` | `g_counter.py` | Monotonically increasing counters |

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All six satisfy: commutativity, associativity, idempotency — the three lattice laws that

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guarantee convergence regardless of message delivery order.

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### When to use CRDT mode

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| Scenario | Recommendation |

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|----------|----------------|

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| Human-paced commits (once per hour/day) | Three-way merge (Phases 1–3) |

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| Many agents writing concurrently (sub-second) | CRDT mode |

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| Shared annotation sets (many simultaneous contributors) | CRDT `ORSet` |

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| Collaborative score editing (DAW-style) | CRDT `RGA` |

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| Per-dimension mix | Set `merge_mode="crdt"` per `CRDTDimensionSpec` |

---

## The Full Plugin Protocol Stack

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```

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MuseDomainPlugin ← required by every domain plugin

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├── schema() ← Phase 2: declare data structure

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├── snapshot() ← capture current live state

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├── diff() ← compute typed StructuredDelta

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├── drift() ← detect uncommitted changes

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├── apply() ← apply delta to working tree

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└── merge() ← three-way merge (fallback)

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StructuredMergePlugin ← optional Phase 3 extension

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└── merge_ops() ← operation-level OT merge

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CRDTPlugin ← optional Phase 4 extension

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├── crdt_schema() ← declare per-dimension CRDT types

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├── join() ← convergent lattice join

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├── to_crdt_state() ← lift plain snapshot to CRDT state

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└── from_crdt_state() ← materialise CRDT state back to snapshot

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```

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The core engine detects capabilities at runtime via `isinstance`:

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```python

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if isinstance(plugin, CRDTPlugin) and schema["merge_mode"] == "crdt":

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return crdt_join_snapshots(plugin, ...)

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elif isinstance(plugin, StructuredMergePlugin):

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return plugin.merge_ops(base, ours_snap, theirs_snap, ours_ops, theirs_ops)

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else:

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return plugin.merge(base, left, right)

```

---

## How CLI Commands Use the Plugin

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| Command | Plugin method(s) called |

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|---------|------------------------|

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| `muse commit` | `snapshot()`, `diff()` (for structured_delta) |

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| `muse status` | `drift()` |

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| `muse diff` | `diff()` |

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| `muse show` | reads stored `structured_delta` |

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| `muse merge` | `merge_ops()` or `merge()` (capability detection) |

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| `muse cherry-pick` | `merge()` |

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| `muse stash` | `snapshot()` |

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| `muse checkout` | `diff()` + `apply()` |

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| `muse domains` | `schema()`, capability introspection |

---

## Adding a New Domain — Quick Reference

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1. Copy `muse/plugins/scaffold/plugin.py` → `muse/plugins/<domain>/plugin.py`

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2. Implement all methods (every `raise NotImplementedError` must be replaced)

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3. Register in `muse/plugins/registry.py`

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4. Run `muse init --domain <domain>` in any project directory

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5. All existing CLI commands work immediately

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See the full [Plugin Authoring Guide](../guide/plugin-authoring-guide.md) for a step-by-step

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walkthrough covering Phases 1–4 with examples.

---

## CLI Command Reference

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Muse uses a **three-tier command architecture**. See [`docs/reference/cli-tiers.md`](../reference/cli-tiers.md) for the full specification and JSON output schemas.

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### Tier 1 — Plumbing (`muse plumbing …`)

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Machine-readable, JSON-outputting, pipeable primitives. Designed for scripts, agents, and CI automation.

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| Command | Description |

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|---------|-------------|

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| `muse plumbing hash-object <file>` | SHA-256 a file; optionally store it |

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| `muse plumbing cat-object <id>` | Emit raw bytes of a stored object |

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| `muse plumbing rev-parse <ref>` | Resolve branch/HEAD/prefix → commit_id |

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| `muse plumbing ls-files [<ref>]` | List tracked files and object IDs |

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| `muse plumbing read-commit <id>` | Emit full commit JSON |

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| `muse plumbing read-snapshot <id>` | Emit full snapshot JSON |

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| `muse plumbing commit-tree <snap_id>` | Create a commit from an explicit snapshot |

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| `muse plumbing update-ref <branch> <id>` | Move a branch HEAD |

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| `muse plumbing commit-graph` | Emit commit DAG as JSON |

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| `muse plumbing pack-objects <ids…>` | Build a PackBundle JSON to stdout |

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| `muse plumbing unpack-objects` | Read PackBundle JSON from stdin, write to store |

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| `muse plumbing ls-remote [remote]` | List branch refs on a remote |

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### Tier 2 — Core Porcelain (top-level `muse …`)

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Human and agent VCS commands. Domain-agnostic; delegate to `muse.core.*`.

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| Command | Description |

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|---------|-------------|

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| `muse init [--domain <name>]` | Initialize a repository |

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| `muse commit -m <msg>` | Snapshot live state and record a commit |

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| `muse status` | Show drift between HEAD and working tree |

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| `muse diff [<base>] [<target>]` | Show delta between commits or vs. working tree |

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| `muse log [--oneline] [--graph] [--stat]` | Display commit history |

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| `muse show [<ref>] [--json] [--stat]` | Inspect a single commit with operation-level detail |

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| `muse branch [<name>] [-d <name>]` | Create or delete branches |

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| `muse checkout <branch\|commit> [-b]` | Switch branches or restore historical state |

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| `muse merge <branch>` | Three-way merge (or CRDT join, capability-detected) |

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| `muse cherry-pick <commit>` | Apply a specific commit's delta on top of HEAD |

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| `muse revert <commit>` | Create a new commit undoing a prior commit |

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| `muse reset <commit> [--hard]` | Move branch pointer |

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| `muse stash` / `pop` / `list` / `drop` | Temporarily shelve uncommitted changes |

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| `muse tag add <tag> [<ref>]` | Tag a commit |

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| `muse tag list [<ref>]` | List tags |

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| `muse domains` | Show domain dashboard — registered domains, capabilities, schema |

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| `muse remote add <name> <url>` | Register a named remote |

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| `muse clone <url> [dir]` | Clone a remote repository |

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| `muse fetch [remote]` | Download commits/snapshots/objects |

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| `muse pull [remote]` | Fetch + three-way merge |

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| `muse push [remote]` | Upload local commits/snapshots/objects |

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| `muse check` | Domain-agnostic invariant check |

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| `muse annotate` | CRDT-backed commit annotations |

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### Tier 3 — Semantic Porcelain

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Domain-specific commands that interpret multidimensional state. Each sub-namespace is served by the corresponding plugin.

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#### MIDI domain (`muse midi …`)

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| Command | Description |

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|---------|-------------|

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| `muse midi notes` | Every note in a track as musical notation |

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| `muse midi note-log` | Note-level commit history |

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| `muse midi note-blame` | Per-bar attribution |

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| `muse midi harmony` | Chord analysis and key detection |

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| `muse midi piano-roll` | ASCII piano roll visualization |

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| `muse midi hotspots` | Bar-level churn leaderboard |

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| `muse midi velocity-profile` | Dynamic range and velocity histogram |

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| `muse midi transpose` | Transpose all notes by N semitones |

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| `muse midi mix` | Combine two MIDI tracks into one |

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| `muse midi query` | MIDI DSL predicate query over history |

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| `muse midi check` | Enforce MIDI invariant rules |

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#### Code domain (`muse code …`)

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| Command | Description |

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|---------|-------------|

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| `muse code symbols` | List every symbol in a snapshot |

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| `muse code symbol-log` | Full history of one symbol |

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| `muse code detect-refactor` | Detect semantic refactoring operations |

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| `muse code grep` | Search the symbol graph |

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| `muse code blame` | Which commit last touched a symbol |

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| `muse code hotspots` | Symbol churn leaderboard |

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| `muse code stable` | Symbol stability leaderboard |

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| `muse code coupling` | File co-change analysis |

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| `muse code compare` | Deep semantic comparison between snapshots |

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| `muse code languages` | Language and symbol-type breakdown |

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| `muse code patch` | Surgical per-symbol modification |

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| `muse code query` | Symbol graph predicate DSL |

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| `muse code query-history` | Temporal symbol search |

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| `muse code deps` | Import graph and call graph |

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| `muse code find-symbol` | Cross-commit symbol search |

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| `muse code impact` | Transitive blast-radius for a symbol |

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| `muse code dead` | Dead code candidates |

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| `muse code coverage` | Interface call-coverage |

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| `muse code lineage` | Full provenance chain of a symbol |

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| `muse code api-surface` | Public API surface at a commit |

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| `muse code codemap` | Semantic topology of the codebase |

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| `muse code clones` | Find duplicate symbols |

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| `muse code checkout-symbol` | Restore a historical symbol version |

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| `muse code semantic-cherry-pick` | Cherry-pick named symbols from history |

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| `muse code index` | Manage local symbol indexes |

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| `muse code breakage` | Detect structural breakage vs HEAD |

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| `muse code invariants` | Enforce architectural rules |

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| `muse code check` | Semantic invariant enforcement |

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#### Coordination domain (`muse coord …`)

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| Command | Description |

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|---------|-------------|

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| `muse coord reserve` | Advisory symbol reservation |

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| `muse coord intent` | Declare an operation before executing |

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| `muse coord forecast` | Predict merge conflicts |

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| `muse coord plan-merge` | Dry-run semantic merge plan |

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| `muse coord shard` | Partition codebase into parallel work zones |

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| `muse coord reconcile` | Recommend merge ordering strategy |

---

## Remote Sync

Muse supports synchronizing repositories with a remote host (e.g. MuseHub)

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through six commands built on a typed, swappable transport layer.

### Commands

| Command | Description |

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|---------|-------------|

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| `muse remote add <name> <url>` | Register a named remote connection |

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| `muse clone <url> [dir]` | Create a local copy of a remote repository |

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| `muse fetch [remote]` | Download commits/snapshots/objects (no merge) |

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| `muse pull [remote]` | Fetch + three-way merge into current branch |

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| `muse push [remote]` | Upload local commits/snapshots/objects |

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| `muse plumbing ls-remote [remote]` | List branch refs on a remote (Tier 1 plumbing) |

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### Transport Architecture

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```

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Muse CLI (client) MuseHub (server)

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───────────────── ────────────────

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MuseTransport Protocol

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└─ HttpTransport (urllib, stdlib) ──HTTPS──► GET {url}/refs

POST {url}/fetch

POST {url}/push

```

The `MuseTransport` Protocol in `muse/core/transport.py` is the seam between

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CLI commands and the HTTP implementation. Every command delegates to this

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Protocol, so MuseHub can upgrade to HTTP/2 or gRPC without touching command

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code — only `HttpTransport` changes.

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### PackBundle Wire Format

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The unit of exchange is a `PackBundle` (defined in `muse/core/pack.py`): a

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JSON object carrying commits, snapshots, and base64-encoded object blobs.

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`build_pack()` assembles a bundle from a set of local commit IDs;

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`apply_pack()` writes a received bundle into the local `.muse/` directory in

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dependency order (objects → snapshots → commits).

```

muse/core/pack.py

├─ build_pack(root, commit_ids, *, have) → PackBundle

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└─ apply_pack(root, bundle) → ApplyResult # commits/snapshots/objects written + skipped

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```

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### Local State for Remotes

```

.muse/

config.toml [remotes.<name>] url + branch

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remotes/<name>/<branch> last-known remote commit ID (tracking head)

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```

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See `docs/reference/remotes.md` for the full reference including the MuseHub

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API contract, authentication, and tracking branch semantics.

---

## Testing & Verification

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```bash

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# Full test suite (1903 tests)

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.venv/bin/pytest tests/ -v

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# Type checking (zero errors required)

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mypy muse/

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# Typing audit (zero Any violations required)

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python tools/typing_audit.py --dirs muse/ tests/ --max-any 0

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```

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CI runs all three gates on every PR to `dev` and on every `dev → main` merge.

---

## Key Design Decisions

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**Why no `async`?** The CLI is synchronous by design. All algorithms are CPU-bound and

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complete in bounded time. If a domain's data is too large to diff synchronously, the plugin

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should chunk it — this is a domain concern, not a core concern.

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**Why TypedDicts over Pydantic?** Zero external dependencies. All types are JSON-serialisable

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by construction. `mypy --strict` verifies them without runtime overhead.

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**Why content-addressed storage?** Objects are never overwritten. Checkout, revert, and

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cherry-pick cost zero bytes when the target objects already exist. The object store scales to

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millions of fine-grained sub-elements (individual notes, nucleotides, mesh vertices) without

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format changes.

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**Why four phases?** Each phase is independently useful. A plugin that only implements

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Phase 1 gets rich operation-level `muse show` output. Phase 2 adds algorithm selection.

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Phase 3 adds sub-file auto-merge. Phase 4 adds convergent multi-agent semantics. Adoption

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is incremental and current.