diff --git a/backend/fluksio/flow/schemas.py b/backend/fluksio/flow/schemas.py
index b877953..40f04c1 100644
--- a/backend/fluksio/flow/schemas.py
+++ b/backend/fluksio/flow/schemas.py
@@ -253,6 +253,12 @@ class FlowOrigin(BaseModel):
     #: a run stamped with a dirty commit names code that was never stored.
     commit: str = ""
     dirty: bool = False
+    #: The file that declared the flow, relative to ``repo``, and the module
+    #: name it was imported under. What ``fluksio run`` imports by default,
+    #: instead of every script below the working directory — by that name, or
+    #: the generated node bodies would change with how the flow was synced.
+    declared_in: str = ""
+    module: str = ""
 
 
 class FlowInput(BaseModel):
diff --git a/backend/fluksio/sdk/__init__.py b/backend/fluksio/sdk/__init__.py
index 5e0cf6b..888edf8 100644
--- a/backend/fluksio/sdk/__init__.py
+++ b/backend/fluksio/sdk/__init__.py
@@ -582,6 +582,35 @@ def _code_of(spec: NodeSpec) -> dict[str, Any]:
     return {"code_files": files, "code_digest": digest_of(files)}
 
 
+def _declared_at() -> tuple[str, str]:
+    """The file and module name of whatever constructed the flow.
+
+    Empty for a declaration no import could reach again: a script run
+    directly, or a notebook cell, which is not a file on disk.
+    """
+    frame = inspect.currentframe()
+    # Out of this helper, then out of `Flow.__init__`.
+    for _ in range(2):
+        frame = frame.f_back if frame is not None else None
+    if frame is None:
+        return "", ""
+    module = str(frame.f_globals.get("__name__") or "")
+    path = Path(frame.f_code.co_filename)
+    if module == "__main__" or not path.is_file():
+        return "", ""
+    return str(path.resolve()), module
+
+
+def _relative(path: str, repo: str) -> str:
+    """``path`` as seen from ``repo``, or empty when it is not inside it."""
+    if not path or not repo:
+        return ""
+    try:
+        return Path(path).relative_to(Path(repo).resolve()).as_posix()
+    except ValueError:
+        return ""
+
+
 def _serialisable(value: Any) -> bool:
     try:
         json.dumps(value)
@@ -619,6 +648,9 @@ class Flow:
         self.inputs = list(inputs)
         self.outputs = list(outputs)
         self.nodes = [_spec_of(entry) for entry in nodes]
+        #: Where this flow was declared: the file, and the module name it was
+        #: imported under. What `fluksio run` imports by default.
+        self.declared_in, self.module = _declared_at()
         self._resolve_types()
         self._validate()
         self._nodes = [_check(spec, mode) for spec in self.nodes]
@@ -719,7 +751,11 @@ class Flow:
             "outputs": self.outputs,
         }
         if origin is not None:
-            doc["origin"] = origin
+            declared_in = _relative(self.declared_in, str(origin.get("repo") or ""))
+            doc["origin"] = origin | {
+                "declared_in": declared_in,
+                "module": self.module if declared_in else "",
+            }
         return doc
 
     def shims(self) -> dict[str, str]:
diff --git a/backend/fluksio/sdk/cli.py b/backend/fluksio/sdk/cli.py
index 242b491..7393d56 100644
--- a/backend/fluksio/sdk/cli.py
+++ b/backend/fluksio/sdk/cli.py
@@ -35,6 +35,7 @@ from fluksio.sdk.client import (
     Client,
     RunHandle,
     data_dir,
+    ignored,
     login,
     origin_of,
     repo_root,
@@ -152,22 +153,28 @@ def _walkable(entry: Path) -> bool:
     )
 
 
-def _below(root: Path) -> Iterator[Path]:
+def _below(root: Path, skip: frozenset[Path] = frozenset()) -> Iterator[Path]:
     """Every module and package under a plain directory, however deep.
 
     One directory per study — `dev/s1_baseline/study.py` — is a layout people
     have, and naming each of them on the command line is bookkeeping the tool
     can do. A package is yielded whole and not descended into: its own walk
     imports its submodules under the right names.
+
+    ``skip`` is what the repository ignores. Importing a module runs it, and
+    what a repository ignores — `mlruns/`, `results/` — is output rather than
+    studies, and often large enough that walking it is most of the cost.
     """
     for entry in sorted(root.iterdir()):
+        if entry in skip:
+            continue
         if entry.is_file() and entry.suffix == ".py":
             yield entry
         elif _walkable(entry):
             if (entry / "__init__.py").exists():
                 yield entry
             else:
-                yield from _below(entry)
+                yield from _below(entry, skip)
 
 
 def _import_package(directory: Path) -> None:
@@ -207,7 +214,7 @@ def discover(targets: list[str], keep_going: bool = False) -> list[Flow]:
         # A plain directory — a repository root, or a directory of studies.
         # Its own modules, the packages inside it, and the same again all the
         # way down, so one folder per study needs no naming.
-        for entry in _below(path):
+        for entry in _below(path, ignored(path)):
             try:
                 if entry.is_dir():
                     _import_package(entry)
@@ -496,7 +503,32 @@ def _params(definition: dict[str, Any], rest: list[str]) -> dict[str, Any]:
     return params
 
 
-def _sync_first(client: Client, targets: list[str] | None = None) -> None:
+def _declaration(client: Client, flow: str) -> tuple[str, str, Path] | None:
+    """Where a flow's last sync found it: import root, module name, file.
+
+    None when there is no such record to go on: a flow never synced, one drawn
+    on the canvas, an engine older than the field, or a checkout where that
+    file is not where the name says.
+    """
+    if not flow:
+        return None
+    stored = client.get_flow(flow) or {}
+    origin = (stored.get("definition") or {}).get("origin") or {}
+    declared_in = str(origin.get("declared_in") or "")
+    module = str(origin.get("module") or "")
+    if not declared_in or not module:
+        return None
+    path = Path(repo_root(".")) / declared_in
+    stem = path.parent if path.name == "__init__.py" else path.with_suffix("")
+    parts = module.split(".")
+    if not path.is_file() or list(stem.parts[-len(parts) :]) != parts:
+        return None
+    return str(stem.parents[len(parts) - 1]), module, path
+
+
+def _sync_first(
+    client: Client, targets: list[str] | None = None, flow: str = ""
+) -> None:
     """Upload what the working directory declares, before running it.
 
     The reason a run exists is usually the edit that came before it, and
@@ -504,24 +536,38 @@ def _sync_first(client: Client, targets: list[str] | None = None) -> None:
     done. So `run` syncs by default — including the worker refresh, which is
     what makes an edit to your own package take effect at all.
 
-    The whole directory, downwards: from a repository root the flow is usually
-    in a study folder below, and the alternative is syncing by hand and then
-    running with `--no-sync`. The upload is already a no-op for a flow nothing
-    changed in, so the cost is importing the other studies — which `--sync`
-    narrows when that is not free.
+    What is synced is the module that declared the flow, as the last sync
+    recorded it. Importing a module runs it, so walking the working directory
+    would run every analysis script in it before the run was even submitted.
+    A flow with no such record — never synced, or an engine older than the
+    field — falls back to the whole directory, downwards, skipping what the
+    repository ignores; a study there that will not import is a warning.
+    `--sync` names the targets outright.
 
     A directory that declares nothing is not an error: a flow drawn on the
     canvas is run the same way, and has nothing to upload.
     """
+    declared = None if targets else _declaration(client, flow)
     try:
-        flows = discover(targets or ["."], keep_going=True)
-    except (ImportError, SyncError) as exc:
+        if declared is None:
+            flows = discover(targets or ["."], keep_going=True)
+        else:
+            # Under the name it was synced with, so the node bodies it
+            # generates are the ones already stored.
+            _import(*declared)
+            flows = list(FLOWS.values())
+    except SyncError as exc:
         # Do not fail a run for a module the run may not even need.
         _say(f"warning: nothing synced — {exc}")
         return
+    except Exception as exc:
+        # A module named outright is imported without the walk's forgiveness,
+        # and importing it runs it: this is whatever it raised at its top.
+        _say(f"warning: nothing synced — {type(exc).__name__}: {exc}")
+        return
     if not flows:
         return
-    repo = repo_root((targets or ["."])[0])
+    repo = repo_root(declared[2] if declared else (targets or ["."])[0])
     reports = sync(flows, client, origin=origin_of(repo))
     changed = [r for r in reports if not r.unchanged]
     if changed:
@@ -606,7 +652,7 @@ def cmd_run(args: argparse.Namespace, rest: list[str]) -> int:
     try:
         with _client_for(args) as client:
             if not args.no_sync:
-                _sync_first(client, args.sync)
+                _sync_first(client, args.sync, args.flow)
             stored = client.get_flow(args.flow)
             if stored is None:
                 return _fail(f"no flow '{args.flow}' on that engine")
@@ -1145,7 +1191,7 @@ def cmd_sweep(args: argparse.Namespace) -> int:
     try:
         with _client_for(args) as client:
             if not args.no_sync:
-                _sync_first(client, args.sync)
+                _sync_first(client, args.sync, args.flow)
             stored = client.get_flow(args.flow)
             if stored is None:
                 return _fail(f"no flow '{args.flow}' on that engine")
diff --git a/backend/fluksio/sdk/client.py b/backend/fluksio/sdk/client.py
index 7c57bfb..77cd89c 100644
--- a/backend/fluksio/sdk/client.py
+++ b/backend/fluksio/sdk/client.py
@@ -708,6 +708,26 @@ def repo_root(start: str | Path) -> str:
     return found or str(directory)
 
 
+def ignored(directory: Path) -> frozenset[Path]:
+    """What the repository ignores below a directory, as git itself reads it.
+
+    Directories come back whole rather than file by file, so an ignored
+    `mlruns/` costs one entry instead of a walk. Empty outside a repository.
+    """
+    listed = _git(
+        str(directory),
+        "ls-files",
+        "--others",
+        "--ignored",
+        "--exclude-standard",
+        "--directory",
+        "-z",
+    )
+    return frozenset(
+        directory / entry.rstrip("/") for entry in (listed or "").split("\0") if entry
+    )
+
+
 def sync(
     flows: Iterable[Flow],
     client: Client,
diff --git a/backend/tests/sdk/test_build.py b/backend/tests/sdk/test_build.py
index 2f68b3d..672bc5b 100644
--- a/backend/tests/sdk/test_build.py
+++ b/backend/tests/sdk/test_build.py
@@ -376,3 +376,23 @@ def test_the_registry_and_the_builder_come_with_the_authoring_import():
     assert fluksio.FLOWS is fluksio.sdk.FLOWS
     assert fluksio.FLOWS["train"] is flow
     assert fluksio.build(flow) == fluksio.sdk.build(flow)
+
+
+def test_a_flow_records_the_module_that_declared_it():
+    """What `fluksio run` imports by default, rather than the whole tree."""
+    from pathlib import Path
+
+    here = Path(__file__).resolve()
+    flow = a_flow()
+
+    assert flow.declared_in == str(here)
+    assert flow.module == __name__
+
+    origin = flow.document({"kind": "python", "repo": str(here.parents[2])})["origin"]
+    assert origin["declared_in"] == "tests/sdk/test_build.py"
+    assert origin["module"] == __name__
+    assert FlowDef.model_validate(flow.document(origin)).origin.module == __name__
+
+    # A repository the file is not in has no path to give it.
+    elsewhere = flow.document({"kind": "python", "repo": "/elsewhere"})["origin"]
+    assert (elsewhere["declared_in"], elsewhere["module"]) == ("", "")
diff --git a/backend/tests/test_cli.py b/backend/tests/test_cli.py
index cb74c49..9202efa 100644
--- a/backend/tests/test_cli.py
+++ b/backend/tests/test_cli.py
@@ -550,6 +550,85 @@ def test_a_study_per_directory_imports_under_its_own_name(tmp_path) -> None:
         sys.path[:] = [entry for entry in sys.path if entry != str(tmp_path / "dev")]
 
 
+def test_run_imports_the_module_that_declared_the_flow(tmp_path, monkeypatch):
+    """Not every script below the working directory: importing one runs it.
+
+    Imported under the name the last sync recorded, so the node bodies it
+    generates are the ones already stored. With nothing recorded, the walk.
+    """
+    from fluksio.sdk import cli as sdk_cli
+
+    study = tmp_path / "dev" / "s1" / "study.py"
+    study.parent.mkdir(parents=True)
+    study.write_text("")
+    monkeypatch.chdir(tmp_path)
+
+    imported: list[tuple] = []
+    walked: list[list[str]] = []
+    monkeypatch.setattr(sdk_cli, "_import", lambda *args: imported.append(args))
+    monkeypatch.setattr(
+        sdk_cli,
+        "discover",
+        lambda targets, keep_going=False: walked.append(targets) or [],
+    )
+
+    class Engine:
+        origin: dict = {}
+
+        def get_flow(self, name):
+            return {"definition": {"origin": self.origin}}
+
+    engine = Engine()
+    engine.origin = {"declared_in": "dev/s1/study.py", "module": "s1.study"}
+    sdk_cli._sync_first(engine, [], "study")
+    assert imported == [
+        (str(tmp_path / "dev"), "s1.study", tmp_path / "dev" / "s1" / "study.py")
+    ]
+    assert walked == []
+
+    # A name that does not match the file is not trusted, and neither is a
+    # file this checkout does not have: both walk, as an unrecorded flow does.
+    for origin in (
+        {"declared_in": "dev/s1/study.py", "module": "s2.study"},
+        {"declared_in": "dev/s9/study.py", "module": "s9.study"},
+        {},
+    ):
+        engine.origin = origin
+        sdk_cli._sync_first(engine, [], "study")
+    assert walked == [["."], ["."], ["."]]
+
+    # And `--sync` is taken as said.
+    sdk_cli._sync_first(engine, ["dev/s1"], "study")
+    assert walked[-1] == ["dev/s1"]
+
+
+def test_the_walk_skips_what_the_repository_ignores(tmp_path, monkeypatch) -> None:
+    """`mlruns/` is output, not a study, and importing it would run it."""
+    import shutil
+    import subprocess
+    import sys
+
+    import pytest
+
+    from fluksio.sdk.cli import discover
+
+    if shutil.which("git") is None:
+        pytest.skip("needs git")
+    subprocess.run(["git", "init", "-q", str(tmp_path)], check=True)
+    (tmp_path / ".gitignore").write_text("mlruns/\nscratch.py\n")
+    (tmp_path / "mlruns" / "0").mkdir(parents=True)
+    (tmp_path / "mlruns" / "0" / "boom.py").write_text("raise SystemExit('imported')\n")
+    (tmp_path / "scratch.py").write_text("raise SystemExit('imported')\n")
+    (tmp_path / "walked_study.py").write_text("VALUE = 1\n")
+
+    try:
+        discover([str(tmp_path)])
+        assert sys.modules["walked_study"].VALUE == 1
+    finally:
+        sys.modules.pop("walked_study", None)
+        sys.path[:] = [entry for entry in sys.path if entry != str(tmp_path)]
+
+
 def test_two_files_of_one_name_are_refused(tmp_path) -> None:
     """Python keeps one module per name, and a node's body imports by it.
 
diff --git a/docs/code/cli.md b/docs/code/cli.md
index 488096a..70ae500 100644
--- a/docs/code/cli.md
+++ b/docs/code/cli.md
@@ -308,13 +308,18 @@ upgraded its cache is keyed on the whole repository, as it was before. See
 fluksio run train --lr 0.05 --seed 7 [--wait]
 ```
 
-Syncs the working directory *and everything under it*, then submits a run, so
-the command after an edit is this one and nothing else, from the repository
-root as readily as from the study's own folder. A study that will not import
-is a warning rather than a stopped run; the upload is already a no-op for a
-flow nothing changed in, so what the walk costs is importing the others.
-`--sync dev/s1_baseline` (repeatable) narrows it to what you name when that
-is not free, and `--no-sync` skips it entirely.
+Syncs the flow, then submits a run, so the command after an edit is this one
+and nothing else, from the repository root as readily as from the study's own
+folder. What it imports is the module that declared the flow, as the last
+`sync` recorded it, under the same module name. Importing a module runs it, so
+the other scripts in the repository are left alone.
+
+A flow the engine has no such record for (never synced, drawn on the canvas,
+or on an engine older than the record) syncs the working directory *and
+everything under it* instead, skipping whatever the repository's `.gitignore`
+covers. A study there that will not import is a warning rather than a stopped
+run. `--sync dev/s1_baseline` (repeatable) names what to sync outright, and
+`--no-sync` skips it entirely.
 
 Flags that are not its own are the flow's inputs, typed by what the flow
 declares them as, so a name the flow has not got is refused by name, and
diff --git a/frontend/src/client/schemas.gen.ts b/frontend/src/client/schemas.gen.ts
index ec3cbfa..f846aa5 100644
--- a/frontend/src/client/schemas.gen.ts
+++ b/frontend/src/client/schemas.gen.ts
@@ -1159,6 +1159,16 @@ export const FlowOriginSchema = {
             type: 'boolean',
             title: 'Dirty',
             default: false
+        },
+        declared_in: {
+            type: 'string',
+            title: 'Declared In',
+            default: ''
+        },
+        module: {
+            type: 'string',
+            title: 'Module',
+            default: ''
         }
     },
     type: 'object',
diff --git a/frontend/src/client/types.gen.ts b/frontend/src/client/types.gen.ts
index 4095aee..a10b029 100644
--- a/frontend/src/client/types.gen.ts
+++ b/frontend/src/client/types.gen.ts
@@ -364,6 +364,8 @@ export type FlowOrigin = {
     repo?: string;
     commit?: string;
     dirty?: boolean;
+    declared_in?: string;
+    module?: string;
 };
 
 export type FlowRollup = {