diff --git a/DECISIONS.md b/DECISIONS.md
index e2ea35e..a7edf77 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -559,6 +559,28 @@ without reducing risk. Making `worktree_id` optional lets Smriti surface
 filesystem isolation when contention risk exists while preserving the
 lightweight claim path for work that does not need a separate git index.
 
+### Why canonical project_root lives on RepoModel, lazily backfilled
+
+`CommitModel.project_root` remains per-checkpoint provenance: it records where
+the agent was standing when a checkpoint was written. That is useful context,
+but it is a poor operational anchor for worktrees because "latest checkpoint
+wins" makes the chosen checkout depend on whichever agent wrote state most
+recently.
+
+The canonical worktree anchor belongs on `RepoModel` because it is a property
+of the space as a project, not of an individual chat session, checkpoint, or
+worktree. Sessions and checkpoints can be created from multiple clones; worktree
+rows represent outputs created from an anchor, not the source of truth for the
+next anchor.
+
+Lazy backfill is deliberately preferred over a one-shot migration. Existing
+spaces already have useful checkpoint-level roots, but the database cannot know
+which clone a human wants as canonical without touching the filesystem and
+making an intent guess. On first worktree open, Smriti resolves the known
+checkpoint root, validates it at the point of use, and writes the resolved path
+back to `repos.project_root`. Spaces therefore self-canonicalize through normal
+use while preserving explicit override via `smriti space set-project-root`.
+
 ---
 
 ## Open questions and deferred decisions
diff --git a/REPO_STRUCTURE.md b/REPO_STRUCTURE.md
index 91a489e..7185d34 100644
--- a/REPO_STRUCTURE.md
+++ b/REPO_STRUCTURE.md
@@ -62,14 +62,16 @@ smriti/
 │   ├── config/
 │   │   ├── providers.example.yaml  Template — copy to providers.yaml
 │   │   └── providers.yaml          Your keys (gitignored, not committed)
-│   ├── alembic/                Database migrations (14 versions)
+│   ├── alembic/                Database migrations (15 versions)
 │   ├── tests/
-│   │   ├── integration/        API integration tests (124 tests)
+│   │   ├── integration/        API integration tests (134 tests)
 │   │   │   ├── test_api_v4_chat.py
 │   │   │   ├── test_api_v5_lineage.py
 │   │   │   ├── test_multi_branch_state.py
 │   │   │   ├── test_claims.py
 │   │   │   ├── test_claim_worktree_binding.py
+│   │   │   ├── test_project_root_migration.py
+│   │   │   ├── test_repos_project_root.py
 │   │   │   ├── test_worktrees.py
 │   │   │   ├── test_checkpoint_extract.py
 │   │   │   └── test_delete_endpoints.py
@@ -116,12 +118,13 @@ smriti/
 │   │       ├── template.md     Single source of truth (v2.1, 15 sections)
 │   │       ├── renderer.py     Pure-function render + versioned install
 │   │       └── targets.py      Target configs (claude-code, codex)
-│   └── tests/                  CLI + MCP tests (129 tests)
+│   └── tests/                  CLI + MCP tests (141 tests)
 │       ├── test_branch_close.py
 │       ├── test_init.py
 │       ├── test_mcp_server.py
 │       ├── test_skill_pack.py
 │       ├── test_smoke.py
+│       ├── test_space_cli.py
 │       ├── test_state_multi_branch.py
 │       ├── test_worktree_cli.py
 │       └── test_worktree_mcp.py
@@ -164,11 +167,11 @@ make migration      Create a new migration (usage: make migration msg="...")
 
 ---
 
-## Test counts (as of V3 dirty paths)
+## Test counts (as of V4 project_root canonicalization)
 
 | Suite | Count | Location |
 |---|---|---|
-| Backend integration | 124 | `backend/tests/integration/` |
+| Backend integration | 134 | `backend/tests/integration/` |
 | Backend unit | 129 | `backend/tests/unit/` |
-| CLI + MCP | 129 | `cli/tests/` |
-| **Total** | **382** | |
+| CLI + MCP | 141 | `cli/tests/` |
+| **Total** | **404** | |
diff --git a/backend/alembic/versions/2026_05_04_0300_d1e2f3a4b5c6_add_project_root_to_repos.py b/backend/alembic/versions/2026_05_04_0300_d1e2f3a4b5c6_add_project_root_to_repos.py
new file mode 100644
index 0000000..d623cf4
--- /dev/null
+++ b/backend/alembic/versions/2026_05_04_0300_d1e2f3a4b5c6_add_project_root_to_repos.py
@@ -0,0 +1,27 @@
+"""Add project_root to repos.
+
+Revision ID: d1e2f3a4b5c6
+Revises: c0db5e90f1a2
+Create Date: 2026-05-04 03:00:00.000000
+
+"""
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "d1e2f3a4b5c6"
+down_revision = "c0db5e90f1a2"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "repos",
+        sa.Column("project_root", sa.Text(), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("repos", "project_root")
diff --git a/backend/app/api/routes/chat.py b/backend/app/api/routes/chat.py
index 5dbd0ba..f7eb9a2 100644
--- a/backend/app/api/routes/chat.py
+++ b/backend/app/api/routes/chat.py
@@ -331,6 +331,7 @@ class SpaceBrief(BaseModel):
     id: uuid.UUID
     name: str
     description: Optional[str] = None
+    project_root: Optional[str] = None
 
 
 class ActiveBranchSummary(BaseModel):
@@ -1111,6 +1112,7 @@ def get_space_state(
             id=repo.id,
             name=repo.name,
             description=repo.description,
+            project_root=repo.project_root,
         ),
         head=head_resp,
         commit=commit_resp,
diff --git a/backend/app/api/routes/repos.py b/backend/app/api/routes/repos.py
index 37f7f9a..d120bc1 100644
--- a/backend/app/api/routes/repos.py
+++ b/backend/app/api/routes/repos.py
@@ -1,8 +1,6 @@
+import logging
 import uuid
 from datetime import datetime
-from typing import Annotated
-
-from typing import Optional
 
 from fastapi import APIRouter, Depends, HTTPException, Query, Response
 from pydantic import BaseModel, Field
@@ -10,30 +8,43 @@ from sqlalchemy import select
 from sqlalchemy.orm import Session
 
 from app.db.database import get_db
-from app.db.models import RepoModel, CommitModel
+from app.db.models import CommitModel, RepoModel
 
 router = APIRouter(prefix="/repos", tags=["repos"])
 
 DEMO_USER_ID = uuid.UUID("00000000-0000-0000-0000-00000000000a")
+logger = logging.getLogger("uvicorn.error")
+
 
 class RepoCreate(BaseModel):
     name: str = Field(..., description="Name of the repo/project")
     description: str = Field("", description="Optional description")
+    project_root: str | None = Field(
+        None,
+        description="Canonical project checkout path for worktree operations",
+    )
     user_id: str | None = Field(None, description="Optional user ID, defaults to demo user")
     metadata_: dict = Field(default_factory=dict, alias="metadata")
 
+
+class SetProjectRootRequest(BaseModel):
+    project_root: str
+
+
 class RepoResponse(BaseModel):
     id: uuid.UUID
     repo_slug: str | None
     name: str
     description: str
+    project_root: str | None
     user_id: uuid.UUID
     metadata_: dict = Field(serialization_alias="metadata")
     created_at: datetime
     updated_at: datetime
-    
+
     model_config = {"from_attributes": True}
 
+
 class CommitResponse(BaseModel):
     id: uuid.UUID
     repo_id: uuid.UUID
@@ -59,8 +70,6 @@ class CommitResponse(BaseModel):
 
     model_config = {"from_attributes": True}
 
-import logging
-logger = logging.getLogger("uvicorn.error")
 
 @router.post("", response_model=RepoResponse, status_code=201)
 def create_repo(payload: RepoCreate, db: Session = Depends(get_db)):
@@ -70,7 +79,8 @@ def create_repo(payload: RepoCreate, db: Session = Depends(get_db)):
         user_id=uuid.UUID(payload.user_id) if payload.user_id else DEMO_USER_ID,
         name=payload.name,
         description=payload.description,
-        metadata_=payload.metadata_
+        project_root=payload.project_root,
+        metadata_=payload.metadata_,
     )
     logger.info("before DB call: add")
     db.add(new_repo)
@@ -81,12 +91,36 @@ def create_repo(payload: RepoCreate, db: Session = Depends(get_db)):
     logger.info("after DB call / before response return")
     return new_repo
 
+
 @router.get("", response_model=list[RepoResponse])
 def list_repos(db: Session = Depends(get_db)):
     """List all repos for the current user."""
-    stmt = select(RepoModel).where(RepoModel.user_id == DEMO_USER_ID).order_by(RepoModel.updated_at.desc())
+    stmt = (
+        select(RepoModel)
+        .where(RepoModel.user_id == DEMO_USER_ID)
+        .order_by(RepoModel.updated_at.desc())
+    )
     return db.scalars(stmt).all()
 
+
+@router.patch("/{repo_id}/project-root", response_model=RepoResponse)
+def set_project_root(
+    repo_id: uuid.UUID,
+    payload: SetProjectRootRequest,
+    db: Session = Depends(get_db),
+):
+    """Set the canonical project_root for a space."""
+    repo = db.get(RepoModel, repo_id)
+    if not repo or repo.user_id != DEMO_USER_ID:
+        raise HTTPException(status_code=404, detail="Space not found")
+    if not payload.project_root.strip():
+        raise HTTPException(status_code=400, detail="project_root cannot be empty")
+    repo.project_root = payload.project_root
+    db.commit()
+    db.refresh(repo)
+    return repo
+
+
 @router.get("/{repo_id}", response_model=RepoResponse)
 def get_repo(repo_id: uuid.UUID, db: Session = Depends(get_db)):
     """Get a specific repo."""
@@ -95,10 +129,11 @@ def get_repo(repo_id: uuid.UUID, db: Session = Depends(get_db)):
         raise HTTPException(status_code=404, detail="Repo not found")
     return repo
 
+
 @router.get("/{repo_id}/commits", response_model=list[CommitResponse])
 def list_repo_commits(
     repo_id: uuid.UUID,
-    branch: Optional[str] = Query(None, description="Filter by branch name"),
+    branch: str | None = Query(None, description="Filter by branch name"),
     db: Session = Depends(get_db),
 ):
     """List commits for a repo. Optionally filter by branch name."""
@@ -112,23 +147,27 @@ def list_repo_commits(
     stmt = stmt.order_by(CommitModel.created_at.desc())
     return db.scalars(stmt).all()
 
+
 @router.get("/{repo_id}/commits/latest", response_model=CommitResponse)
 def get_latest_commit(repo_id: uuid.UUID, branch: str = "main", db: Session = Depends(get_db)):
     """Get the latest commit for a repo (and optional branch)."""
     repo = db.get(RepoModel, repo_id)
     if not repo or repo.user_id != DEMO_USER_ID:
         raise HTTPException(status_code=404, detail="Repo not found")
-        
-    stmt = select(CommitModel).where(
-        CommitModel.repo_id == repo_id,
-        CommitModel.branch_name == branch
-    ).order_by(CommitModel.created_at.desc()).limit(1)
-    
+
+    stmt = (
+        select(CommitModel)
+        .where(CommitModel.repo_id == repo_id, CommitModel.branch_name == branch)
+        .order_by(CommitModel.created_at.desc())
+        .limit(1)
+    )
+
     commit = db.scalars(stmt).first()
     if not commit:
         raise HTTPException(status_code=404, detail="No commits found for this repo/branch")
     return commit
 
+
 @router.delete("/{repo_id}", status_code=204)
 def delete_repo(repo_id: uuid.UUID, db: Session = Depends(get_db)) -> Response:
     """Delete a space and cascade to all its commits, sessions, and turns."""
diff --git a/backend/app/api/routes/worktrees.py b/backend/app/api/routes/worktrees.py
index 886844e..7604cc0 100644
--- a/backend/app/api/routes/worktrees.py
+++ b/backend/app/api/routes/worktrees.py
@@ -91,11 +91,30 @@ def _get_repo(space_id: uuid.UUID, db: Session) -> RepoModel:
     return repo
 
 
-def _latest_project_root(space_id: uuid.UUID, db: Session) -> Path:
+def _validate_project_root(project_root: str) -> Path:
+    resolved = Path(project_root).expanduser().resolve()
+    if not resolved.is_dir():
+        raise HTTPException(
+            status_code=400,
+            detail=f"project_root does not exist on disk: {resolved}",
+        )
+    return resolved
+
+
+def _resolve_project_root(repo: RepoModel, db: Session) -> Path:
+    """Resolve the worktree anchor path.
+
+    Prefer the space-level canonical root. For existing spaces without one,
+    fall back to the latest checkpoint root and lazily backfill the canonical
+    field so future worktree opens are no longer agent-activity-dependent.
+    """
+    if repo.project_root:
+        return _validate_project_root(repo.project_root)
+
     stmt = (
         select(CommitModel.project_root)
         .where(
-            CommitModel.repo_id == space_id,
+            CommitModel.repo_id == repo.id,
             CommitModel.project_root.is_not(None),
             CommitModel.project_root != "",
         )
@@ -107,17 +126,16 @@ def _latest_project_root(space_id: uuid.UUID, db: Session) -> Path:
         raise HTTPException(
             status_code=400,
             detail=(
-                "No checkpoint with project_root found for this space; "
-                "create a checkpoint from the project checkout first."
+                "No project_root configured for this space. Set it via "
+                "`smriti space set-project-root <space> <path>` or create a "
+                "checkpoint with project_root set."
             ),
         )
 
-    resolved = Path(project_root).expanduser().resolve()
-    if not resolved.is_dir():
-        raise HTTPException(
-            status_code=400,
-            detail=f"project_root does not exist on disk: {resolved}",
-        )
+    resolved = _validate_project_root(project_root)
+    repo.project_root = str(resolved)
+    db.commit()
+    db.refresh(repo)
     return resolved
 
 
@@ -213,7 +231,7 @@ def create_worktree(
     if not agent:
         raise HTTPException(status_code=400, detail="agent must be non-empty")
 
-    project_root = _latest_project_root(space_id, db)
+    project_root = _resolve_project_root(repo, db)
     suffix = uuid.uuid4().hex[:8]
     branch_name = (payload.branch_name or "").strip() or _default_branch_name(agent, suffix)
     target_path = _resolve_target_path(
@@ -324,7 +342,8 @@ def close_worktree(
             detail=f"Worktree has invalid status: {worktree.status}",
         )
 
-    project_root = _latest_project_root(worktree.repo_id, db)
+    repo = _get_repo(worktree.repo_id, db)
+    project_root = _resolve_project_root(repo, db)
     worktree_path = Path(worktree.path).expanduser().resolve()
 
     if not force:
diff --git a/backend/app/db/models.py b/backend/app/db/models.py
index 98100b1..4ba8935 100644
--- a/backend/app/db/models.py
+++ b/backend/app/db/models.py
@@ -133,6 +133,7 @@ class RepoModel(Base):
     repo_slug: Mapped[str | None] = mapped_column(String(255), unique=True, nullable=True)
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     description: Mapped[str] = mapped_column(Text, default="")
+    project_root: Mapped[str | None] = mapped_column(Text, nullable=True)
     user_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True), nullable=False, index=True
     )
diff --git a/backend/tests/integration/test_multi_branch_state.py b/backend/tests/integration/test_multi_branch_state.py
index 8b790b5..1d0f3ff 100644
--- a/backend/tests/integration/test_multi_branch_state.py
+++ b/backend/tests/integration/test_multi_branch_state.py
@@ -18,8 +18,15 @@ from __future__ import annotations
 # ── Helpers (match the shape used in test_api_v5_lineage.py) ─────────────────
 
 
-def _create_repo(client, name: str = "Multi-Branch State Test"):
-    r = client.post("/api/v2/repos", json={"name": name})
+def _create_repo(
+    client,
+    name: str = "Multi-Branch State Test",
+    project_root: str | None = None,
+):
+    payload = {"name": name}
+    if project_root is not None:
+        payload["project_root"] = project_root
+    r = client.post("/api/v2/repos", json=payload)
     assert r.status_code == 201, r.text
     return r.json()["id"]
 
@@ -85,6 +92,18 @@ def test_state_no_checkpoints(client):
     assert state["divergence"] is None
 
 
+def test_state_space_header_includes_project_root(client):
+    repo_id = _create_repo(
+        client,
+        "Rooted State",
+        project_root="/tmp/rooted-state",
+    )
+
+    state = _get_state(client, repo_id)
+
+    assert state["space"]["project_root"] == "/tmp/rooted-state"
+
+
 def test_state_main_only(client):
     """Single main checkpoint, no forks: main HEAD present, no extensions."""
     repo_id = _create_repo(client, "Main Only")
diff --git a/backend/tests/integration/test_project_root_migration.py b/backend/tests/integration/test_project_root_migration.py
new file mode 100644
index 0000000..254146f
--- /dev/null
+++ b/backend/tests/integration/test_project_root_migration.py
@@ -0,0 +1,43 @@
+"""SQLite-first regression test for the repos.project_root migration."""
+
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+from alembic.migration import MigrationContext
+from alembic.operations import Operations
+from sqlalchemy import create_engine, inspect, text
+
+
+def _load_migration():
+    path = (
+        Path(__file__).parents[2]
+        / "alembic"
+        / "versions"
+        / "2026_05_04_0300_d1e2f3a4b5c6_add_project_root_to_repos.py"
+    )
+    spec = importlib.util.spec_from_file_location("project_root_migration", path)
+    assert spec and spec.loader
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_project_root_migration_upgrade_and_downgrade_on_sqlite(monkeypatch):
+    migration = _load_migration()
+    engine = create_engine("sqlite://")
+
+    with engine.begin() as conn:
+        conn.execute(text("CREATE TABLE repos (id VARCHAR PRIMARY KEY)"))
+        context = MigrationContext.configure(conn)
+        operations = Operations(context)
+        monkeypatch.setattr(migration, "op", operations)
+
+        migration.upgrade()
+        columns = {c["name"]: c for c in inspect(conn).get_columns("repos")}
+        assert columns["project_root"]["nullable"] is True
+
+        migration.downgrade()
+        columns = {c["name"] for c in inspect(conn).get_columns("repos")}
+        assert "project_root" not in columns
diff --git a/backend/tests/integration/test_repos_project_root.py b/backend/tests/integration/test_repos_project_root.py
new file mode 100644
index 0000000..2ac8963
--- /dev/null
+++ b/backend/tests/integration/test_repos_project_root.py
@@ -0,0 +1,73 @@
+"""Regression coverage for canonical project_root on spaces."""
+
+from __future__ import annotations
+
+import uuid
+
+
+def test_create_repo_with_project_root(client):
+    r = client.post(
+        "/api/v2/repos",
+        json={"name": "Rooted Repo", "project_root": "/tmp/rooted-repo"},
+    )
+
+    assert r.status_code == 201, r.text
+    assert r.json()["project_root"] == "/tmp/rooted-repo"
+
+
+def test_create_repo_without_project_root(client):
+    r = client.post("/api/v2/repos", json={"name": "No Root Repo"})
+
+    assert r.status_code == 201, r.text
+    assert r.json()["project_root"] is None
+
+
+def test_set_project_root_endpoint(client):
+    created = client.post("/api/v2/repos", json={"name": "Patch Root"}).json()
+
+    r = client.patch(
+        f"/api/v2/repos/{created['id']}/project-root",
+        json={"project_root": "/tmp/patched-root"},
+    )
+
+    assert r.status_code == 200, r.text
+    assert r.json()["project_root"] == "/tmp/patched-root"
+
+
+def test_set_project_root_empty_rejected(client):
+    created = client.post("/api/v2/repos", json={"name": "Empty Root"}).json()
+
+    r = client.patch(
+        f"/api/v2/repos/{created['id']}/project-root",
+        json={"project_root": "   "},
+    )
+
+    assert r.status_code == 400
+    assert "project_root cannot be empty" in r.json()["detail"]
+
+
+def test_set_project_root_nonexistent_repo(client):
+    r = client.patch(
+        f"/api/v2/repos/{uuid.uuid4()}/project-root",
+        json={"project_root": "/tmp/missing"},
+    )
+
+    assert r.status_code == 404
+    assert "Space not found" in r.json()["detail"]
+
+
+def test_repo_responses_include_project_root(client):
+    created = client.post(
+        "/api/v2/repos",
+        json={"name": "Response Root", "project_root": "/tmp/response-root"},
+    ).json()
+
+    fetched = client.get(f"/api/v2/repos/{created['id']}")
+    listed = client.get("/api/v2/repos")
+
+    assert fetched.status_code == 200, fetched.text
+    assert fetched.json()["project_root"] == "/tmp/response-root"
+    assert any(
+        repo["id"] == created["id"] and repo["project_root"] == "/tmp/response-root"
+        for repo in listed.json()
+    )
diff --git a/backend/tests/integration/test_worktrees.py b/backend/tests/integration/test_worktrees.py
index 13b7fc2..eaaab22 100644
--- a/backend/tests/integration/test_worktrees.py
+++ b/backend/tests/integration/test_worktrees.py
@@ -29,8 +29,11 @@ def _git(repo: Path, *args: str, check: bool = True) -> subprocess.CompletedProc
     return result
 
 
-def _create_repo(client, name="Worktree Test Repo"):
-    r = client.post("/api/v2/repos", json={"name": name})
+def _create_repo(client, name="Worktree Test Repo", project_root: str | None = None):
+    payload = {"name": name}
+    if project_root is not None:
+        payload["project_root"] = project_root
+    r = client.post("/api/v2/repos", json=payload)
     assert r.status_code == 201, r.text
     return r.json()["id"]
 
@@ -144,6 +147,62 @@ def test_create_worktree_existing_branch_rejected_without_row_or_directory(
     assert client.get(f"/api/v5/worktrees?space_id={space_id}").json() == []
 
 
+def test_create_worktree_uses_canonical_project_root(client, tmp_path):
+    canonical_repo = _init_git_repo(tmp_path, name="canonical-project")
+    fallback_repo = _init_git_repo(tmp_path, name="fallback-project")
+    repo_id = _create_repo(
+        client,
+        name="Canonical Root Repo",
+        project_root=str(canonical_repo),
+    )
+    session_id = _create_session(client, repo_id)
+    _commit_with_root(client, repo_id, session_id, fallback_repo)
+    target = tmp_path / "canonical-worktree"
+
+    r = _create_worktree(
+        client,
+        repo_id,
+        branch_name="feature/canonical-root",
+        base_path=str(target),
+    )
+
+    assert r.status_code == 201, r.text
+    assert target.exists()
+    assert (
+        _git(canonical_repo, "show-ref", "--verify", "refs/heads/feature/canonical-root")
+        .returncode
+        == 0
+    )
+    assert (
+        _git(
+            fallback_repo,
+            "show-ref",
+            "--verify",
+            "refs/heads/feature/canonical-root",
+            check=False,
+        ).returncode
+        != 0
+    )
+
+
+def test_create_worktree_lazy_backfills_project_root_from_commit(client, tmp_path):
+    git_repo = _init_git_repo(tmp_path)
+    repo_id = _create_project_with_root(client, git_repo)
+    assert client.get(f"/api/v2/repos/{repo_id}").json()["project_root"] is None
+
+    r = _create_worktree(
+        client,
+        repo_id,
+        branch_name="feature/lazy-backfill",
+        base_path=str(tmp_path / "lazy-backfill-worktree"),
+    )
+
+    assert r.status_code == 201, r.text
+    assert client.get(f"/api/v2/repos/{repo_id}").json()["project_root"] == str(
+        git_repo.resolve()
+    )
+
+
 def test_list_show_and_close_clean_worktree(client, tmp_path):
     git_repo = _init_git_repo(tmp_path)
     space_id = _create_project_with_root(client, git_repo)
@@ -284,6 +343,7 @@ def test_create_worktree_requires_project_root(client, tmp_path):
 
     assert r.status_code == 400
     assert "project_root" in r.json()["detail"]
+    assert "set-project-root" in r.json()["detail"]
     assert not target.exists()
 
 
@@ -316,8 +376,8 @@ def test_git_infrastructure_error_does_not_write_row_or_leave_target(
     assert client.get(f"/api/v5/worktrees?space_id={space_id}").json() == []
 
 
-def _init_git_repo(tmp_path: Path) -> Path:
-    repo = tmp_path / "project"
+def _init_git_repo(tmp_path: Path, name: str = "project") -> Path:
+    repo = tmp_path / name
     repo.mkdir()
     _git(repo, "init")
     _git(repo, "config", "user.email", "test@example.com")
diff --git a/cli/smriti_cli/client.py b/cli/smriti_cli/client.py
index 9d32dbf..a4ceff7 100644
--- a/cli/smriti_cli/client.py
+++ b/cli/smriti_cli/client.py
@@ -86,11 +86,26 @@ class SmritiClient:
     def get_space(self, space_id: str) -> dict:
         return self._request("GET", f"/api/v2/repos/{space_id}")
 
-    def create_space(self, name: str, description: str = "") -> dict:
+    def create_space(
+        self,
+        name: str,
+        description: str = "",
+        project_root: str | None = None,
+    ) -> dict:
+        payload = {"name": name, "description": description}
+        if project_root is not None:
+            payload["project_root"] = project_root
         return self._request(
             "POST",
             "/api/v2/repos",
-            json={"name": name, "description": description},
+            json=payload,
+        )
+
+    def set_project_root(self, space_id: str, path: str) -> dict:
+        return self._request(
+            "PATCH",
+            f"/api/v2/repos/{space_id}/project-root",
+            json={"project_root": path},
         )
 
     def delete_space(self, space_id: str) -> None:
diff --git a/cli/smriti_cli/formatters.py b/cli/smriti_cli/formatters.py
index e1d04e7..f711d19 100644
--- a/cli/smriti_cli/formatters.py
+++ b/cli/smriti_cli/formatters.py
@@ -404,6 +404,9 @@ def format_state_brief(
     parts.append(f"# {space.get('name', 'Untitled space')}\n")
     if space.get("description"):
         parts.append(space["description"].rstrip() + "\n")
+    canonical_project_root = _pretty_path(space.get("project_root"))
+    if canonical_project_root:
+        parts.append(f"Project root: {canonical_project_root}\n")
 
     commit_hash = commit.get("commit_hash")
     created_at = commit.get("created_at") or head.get("commit_hash") or ""
diff --git a/cli/smriti_cli/main.py b/cli/smriti_cli/main.py
index 4b7d527..ceb7981 100644
--- a/cli/smriti_cli/main.py
+++ b/cli/smriti_cli/main.py
@@ -3,7 +3,8 @@
 Commands for agent and programmatic use:
 
     smriti space list
-    smriti space create <name> [--description]
+    smriti space create <name> [--description] [--project-root <path>] [--no-project-root]
+    smriti space set-project-root <space> <path>
     smriti space delete <space> [-y]
     smriti state <space> [--preview]
     smriti fork <checkpoint-id> [--branch <name>]
@@ -161,11 +162,39 @@ def cmd_space_list(client: SmritiClient, args: argparse.Namespace) -> None:
 
 
 def cmd_space_create(client: SmritiClient, args: argparse.Namespace) -> None:
-    space = client.create_space(name=args.name, description=args.description or "")
+    if args.no_project_root:
+        project_root: str | None = None
+    elif args.project_root:
+        project_root = args.project_root
+    else:
+        project_root = os.getcwd()
+
+    space = client.create_space(
+        name=args.name,
+        description=args.description or "",
+        project_root=project_root,
+    )
     if args.json:
         _print_json(space)
     else:
         print(f"Created space: {space['name']}  `{space['id']}`")
+        if project_root is not None:
+            print(f"Project root: {project_root}")
+
+
+def cmd_space_set_project_root(client: SmritiClient, args: argparse.Namespace) -> None:
+    space = client.resolve_space(args.space)
+    if args.here or args.path in {".", "--here"}:
+        path = os.getcwd()
+    elif args.path:
+        path = args.path
+    else:
+        _fail("error: path is required unless --here is passed")
+    updated = client.set_project_root(space["id"], path)
+    if args.json:
+        _print_json(updated)
+    else:
+        print(f"Set project_root for '{updated['name']}' to {updated['project_root']}")
 
 
 def cmd_space_delete(client: SmritiClient, args: argparse.Namespace) -> None:
@@ -262,6 +291,8 @@ def _print_no_checkpoints(space: dict, args: argparse.Namespace) -> None:
     print(f"# {space.get('name', 'Untitled space')}")
     if space.get("description"):
         print(space["description"])
+    if space.get("project_root"):
+        print(f"Project root: {space['project_root']}")
     print()
     print("No checkpoints yet. Create one with `smriti checkpoint create`.")
 
@@ -966,9 +997,40 @@ def _build_parser() -> argparse.ArgumentParser:
     sp_create = space_sub.add_parser("create", help="Create a new space")
     sp_create.add_argument("name", help="Space name")
     sp_create.add_argument("--description", help="Optional description", default="")
+    root_group = sp_create.add_mutually_exclusive_group()
+    root_group.add_argument(
+        "--project-root",
+        help="Canonical project checkout path for worktree operations "
+        "(default: current working directory)",
+    )
+    root_group.add_argument(
+        "--no-project-root",
+        action="store_true",
+        help="Leave the space without a canonical project_root",
+    )
     sp_create.add_argument("--json", action="store_true", help="Output structured JSON")
     sp_create.set_defaults(func=cmd_space_create)
 
+    sp_set_project_root = space_sub.add_parser(
+        "set-project-root",
+        help="Set a space's canonical project_root",
+    )
+    sp_set_project_root.add_argument("space", help="Space name or UUID")
+    sp_set_project_root.add_argument(
+        "path",
+        nargs="?",
+        help="Project checkout path. Use '.' for the current directory.",
+    )
+    sp_set_project_root.add_argument(
+        "--here",
+        action="store_true",
+        help="Set project_root to the current directory.",
+    )
+    sp_set_project_root.add_argument(
+        "--json", action="store_true", help="Output structured JSON"
+    )
+    sp_set_project_root.set_defaults(func=cmd_space_set_project_root)
+
     sp_delete = space_sub.add_parser(
         "delete",
         help="Delete a space and all its checkpoints, sessions, and turns",
diff --git a/cli/tests/test_space_cli.py b/cli/tests/test_space_cli.py
new file mode 100644
index 0000000..14a1774
--- /dev/null
+++ b/cli/tests/test_space_cli.py
@@ -0,0 +1,197 @@
+from __future__ import annotations
+
+import argparse
+from unittest.mock import MagicMock
+
+import pytest
+
+from smriti_cli import main as cli_main
+from smriti_cli.client import SmritiClient
+
+
+def _space_dict(**overrides):
+    base = {
+        "id": "space-uuid",
+        "name": "my-project",
+        "description": "",
+        "project_root": "/tmp/project",
+    }
+    base.update(overrides)
+    return base
+
+
+def test_space_create_parser_wiring():
+    parser = cli_main._build_parser()
+
+    args = parser.parse_args(
+        [
+            "space",
+            "create",
+            "my-project",
+            "--description",
+            "Test",
+            "--project-root",
+            "/tmp/project",
+        ]
+    )
+
+    assert args.command == "space"
+    assert args.subcommand == "create"
+    assert args.name == "my-project"
+    assert args.description == "Test"
+    assert args.project_root == "/tmp/project"
+    assert args.no_project_root is False
+    assert args.func is cli_main.cmd_space_create
+
+
+def test_space_create_parser_supports_no_project_root():
+    parser = cli_main._build_parser()
+
+    args = parser.parse_args(["space", "create", "my-project", "--no-project-root"])
+
+    assert args.project_root is None
+    assert args.no_project_root is True
+
+
+def test_space_set_project_root_parser_wiring():
+    parser = cli_main._build_parser()
+
+    args = parser.parse_args(
+        ["space", "set-project-root", "my-project", "/tmp/project"]
+    )
+
+    assert args.command == "space"
+    assert args.subcommand == "set-project-root"
+    assert args.space == "my-project"
+    assert args.path == "/tmp/project"
+    assert args.here is False
+    assert args.func is cli_main.cmd_space_set_project_root
+
+
+def test_space_set_project_root_parser_supports_here_flag():
+    parser = cli_main._build_parser()
+
+    args = parser.parse_args(["space", "set-project-root", "my-project", "--here"])
+
+    assert args.path is None
+    assert args.here is True
+
+
+def test_cmd_space_create_defaults_project_root_to_cwd(
+    tmp_path,
+    monkeypatch,
+    capsys: pytest.CaptureFixture[str],
+):
+    monkeypatch.chdir(tmp_path)
+    client = MagicMock(spec=SmritiClient)
+    client.create_space.return_value = _space_dict(project_root=str(tmp_path))
+    args = argparse.Namespace(
+        name="my-project",
+        description="",
+        project_root=None,
+        no_project_root=False,
+        json=False,
+    )
+
+    cli_main.cmd_space_create(client, args)
+
+    out = capsys.readouterr().out
+    assert "Created space: my-project" in out
+    assert f"Project root: {tmp_path}" in out
+    client.create_space.assert_called_once_with(
+        name="my-project",
+        description="",
+        project_root=str(tmp_path),
+    )
+
+
+def test_cmd_space_create_passes_explicit_project_root():
+    client = MagicMock(spec=SmritiClient)
+    client.create_space.return_value = _space_dict(project_root="/tmp/explicit")
+    args = argparse.Namespace(
+        name="my-project",
+        description="Test",
+        project_root="/tmp/explicit",
+        no_project_root=False,
+        json=False,
+    )
+
+    cli_main.cmd_space_create(client, args)
+
+    client.create_space.assert_called_once_with(
+        name="my-project",
+        description="Test",
+        project_root="/tmp/explicit",
+    )
+
+
+def test_cmd_space_create_can_leave_project_root_null(
+    capsys: pytest.CaptureFixture[str],
+):
+    client = MagicMock(spec=SmritiClient)
+    client.create_space.return_value = _space_dict(project_root=None)
+    args = argparse.Namespace(
+        name="my-project",
+        description="",
+        project_root=None,
+        no_project_root=True,
+        json=False,
+    )
+
+    cli_main.cmd_space_create(client, args)
+
+    out = capsys.readouterr().out
+    assert "Project root:" not in out
+    client.create_space.assert_called_once_with(
+        name="my-project",
+        description="",
+        project_root=None,
+    )
+
+
+def test_cmd_space_set_project_root_calls_patch(capsys: pytest.CaptureFixture[str]):
+    client = MagicMock(spec=SmritiClient)
+    client.resolve_space.return_value = _space_dict(id="space-uuid", name="my-project")
+    client.set_project_root.return_value = _space_dict(
+        id="space-uuid",
+        name="my-project",
+        project_root="/tmp/project",
+    )
+    args = argparse.Namespace(
+        space="my-project",
+        path="/tmp/project",
+        here=False,
+        json=False,
+    )
+
+    cli_main.cmd_space_set_project_root(client, args)
+
+    assert (
+        capsys.readouterr().out == "Set project_root for 'my-project' to /tmp/project\n"
+    )
+    client.resolve_space.assert_called_once_with("my-project")
+    client.set_project_root.assert_called_once_with("space-uuid", "/tmp/project")
+
+
+def test_cmd_space_set_project_root_dot_resolves_cwd(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    client = MagicMock(spec=SmritiClient)
+    client.resolve_space.return_value = _space_dict(id="space-uuid")
+    client.set_project_root.return_value = _space_dict(project_root=str(tmp_path))
+    args = argparse.Namespace(space="my-project", path=".", here=False, json=False)
+
+    cli_main.cmd_space_set_project_root(client, args)
+
+    client.set_project_root.assert_called_once_with("space-uuid", str(tmp_path))
+
+
+def test_cmd_space_set_project_root_here_flag_resolves_cwd(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    client = MagicMock(spec=SmritiClient)
+    client.resolve_space.return_value = _space_dict(id="space-uuid")
+    client.set_project_root.return_value = _space_dict(project_root=str(tmp_path))
+    args = argparse.Namespace(space="my-project", path=None, here=True, json=False)
+
+    cli_main.cmd_space_set_project_root(client, args)
+
+    client.set_project_root.assert_called_once_with("space-uuid", str(tmp_path))
diff --git a/cli/tests/test_state_multi_branch.py b/cli/tests/test_state_multi_branch.py
index d15540b..511439d 100644
--- a/cli/tests/test_state_multi_branch.py
+++ b/cli/tests/test_state_multi_branch.py
@@ -104,6 +104,28 @@ def test_format_state_brief_empty_branches_and_no_divergence_elided():
     assert "## Divergence signal" not in out
 
 
+def test_format_state_brief_shows_canonical_project_root():
+    space = _base_space()
+    space["project_root"] = "/tmp/canonical-project"
+    commit = _base_commit()
+
+    out = format_state_brief(space, _base_head(), commit)
+
+    assert "Project root: /tmp/canonical-project" in out
+    assert "Latest checkpoint:" in out
+    assert "at `/tmp/test-project`" in out
+
+
+def test_format_state_brief_omits_project_root_line_when_null():
+    space = _base_space()
+    space["project_root"] = None
+
+    out = format_state_brief(space, _base_head(), _base_commit())
+
+    assert "Project root:" not in out
+    assert "at `/tmp/test-project`" in out
+
+
 def test_format_state_brief_active_branches_only():
     """Non-empty active_branches → Active branches section appears,
     Divergence signal section absent."""