feat(coverage): the line names standing work with 0 unclassified + derive_new, copies that joined a family since the previous refresh (#2899, milestone 299 step 1)

Since the scoped bucket (#2869) the ledger reads 100% accounted while 439
derive rows stand; the standing block was gated on unclassified > 0 and so
went silent. Build it whatever the todo count ("; standing: ..."), and add
derive_new — derive-grouped rows first seen after the previous refresh
stamp — so entering a project names the drift ("+2 new copies since last
refresh: .error-msg in InceptionCard.vue") instead of waiting for an audit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/mcp/tools/shapes.py

@@ -295,7 +295,9 @@ async def refresh_pattern_coverage(project_id: int) -> dict:
     Returns the accounting payload — total, accounted, counts by status,
     unclassified, repos, largest_gaps, `proposed` (canon proposals awaiting
     confirmation), `derive_groups` (the biggest repeats-with-no-canon
-    families), `proposer` (what this refresh examined) — plus
+    families), `derive_new` (copies that joined a family since the previous
+    refresh — the drift to act on now: derive the canon, don't queue an
+    audit), `proposer` (what this refresh examined) — plus
     `pattern_coverage`, the same one-line summary enter_project carries.
     """
     uid = current_user_id()

src/scribe/services/coverage.py

@@ -462,15 +462,20 @@ async def compute_coverage(
         await shape_ledger.apply_derive_groups(project_id)
     except Exception:
         logger.warning("derive-first grouping failed", exc_info=True)
-    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
-    # where a canon dominates. The previous computation's stamp is the cache;
-    # a first seed has none, so it flags nothing (everything is new then).
+    # "Since the previous computation" — the cache's stamp. A first seed has
+    # none, so nothing is new then. Read once; two passes use it: the
+    # button-B flag (#2793) and the derive-new drift count (#2899).
+    since = None
     try:
         previous = await get_setting(user_id, f"{_CACHE_KEY_PREFIX}{project_id}")
-        since = None
         if previous:
             stamp = (json.loads(previous) or {}).get("computed_at")
             since = datetime.fromisoformat(stamp) if stamp else None
+    except Exception:
+        logger.warning("previous coverage stamp unreadable", exc_info=True)
+    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
+    # where a canon dominates.
+    try:
         await shape_ledger.flag_divergence(project_id, since=since)
     except Exception:
         logger.warning("divergence pass failed", exc_info=True)
@@ -491,6 +496,7 @@ async def compute_coverage(
     unclassified = counts.pop("unclassified")
     proposals = shape_ledger.proposal_summary(rows)
     divergence = shape_ledger.divergence_summary(rows)
+    derive_new = shape_ledger.derive_new_summary(rows, since=since)
     return {
         "total": len(rows),
         "accounted": len(rows) - unclassified,
@@ -501,6 +507,10 @@ async def compute_coverage(
         "proposed": proposals["proposed"],
         "derive_groups": proposals["derive_groups"],
         "top_canon": proposals.get("top_canon"),
+        # Drift since the previous refresh (#2899): copies that joined a
+        # duplicate family — what the arrival line names so drift is noticed
+        # on entering, not found by an audit.
+        "derive_new": derive_new,
         "proposer": proposer_stats,
         # The divergence readout (#2793): button B where button A is canon,
         # and judged shapes whose bodies moved since they were judged.
@@ -648,29 +658,46 @@ def coverage_line(coverage: dict) -> str:
         line += f" — {breakdown}"
     line += f" (estimate{', computed ' + day if day else ''})"
     unclassified = coverage.get("unclassified", 0)
+    # The standing work, built whatever the todo count (#2899). Since the
+    # scoped bucket (#2869) a ledger can read 100% accounted and still carry
+    # derive groups, proposals and divergence; gating this block on
+    # `unclassified > 0` is how 439 derive rows went unmentioned.
+    standing = []
+    if coverage.get("proposed"):
+        standing.append(f"{coverage['proposed']} proposed")
+    n_groups = len(coverage.get("derive_groups") or [])
+    if n_groups:
+        standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
+    # Drift since the previous refresh: copies that joined a family, the
+    # first one named — the sentence the arrival moment exists to say.
+    new = coverage.get("derive_new") or {}
+    if new.get("count"):
+        n = new["count"]
+        first_new = (new.get("examples") or [{}])[0]
+        where = (
+            f": {first_new['label']} in {first_new['path']}"
+            if first_new.get("label") and first_new.get("path") else ""
+        )
+        standing.append(f"+{n} new cop{'y' if n == 1 else 'ies'} since last refresh{where}")
+    if coverage.get("divergent"):
+        standing.append(f"{coverage['divergent']} DIVERGENT")
+    # The next action, on the line (#2874): the canon with the biggest
+    # queue to confirm, and the widest body-identical copy to consolidate.
+    top = coverage.get("top_canon") or {}
+    if top.get("snippet_id"):
+        standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
+    first = (coverage.get("derive_groups") or [{}])[0]
+    if first.get("label") and first.get("files"):
+        standing.append(f"top copy {first['label']} ×{first['files']} files")
     if unclassified:
         line += f"; {unclassified} unclassified"
-        standing = []
-        if coverage.get("proposed"):
-            standing.append(f"{coverage['proposed']} proposed")
-        n_groups = len(coverage.get("derive_groups") or [])
-        if n_groups:
-            standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
-        if coverage.get("divergent"):
-            standing.append(f"{coverage['divergent']} DIVERGENT")
-        # The next action, on the line (#2874): the canon with the biggest
-        # queue to confirm, and the widest body-identical copy to consolidate.
-        top = coverage.get("top_canon") or {}
-        if top.get("snippet_id"):
-            standing.append(f"top canon #{top['snippet_id']} ×{top.get('count', 0)}")
-        first = (coverage.get("derive_groups") or [{}])[0]
-        if first.get("label") and first.get("files"):
-            standing.append(f"top copy {first['label']} ×{first['files']} files")
         if standing:
             line += f" ({', '.join(standing)})"
         gaps = [g["dir"] for g in coverage.get("largest_gaps") or []]
         if gaps:
             line += ", largest: " + ", ".join(gaps)
+    elif standing:
+        line += f"; standing: {', '.join(standing)}"
     if coverage.get("recheck"):
         line += f"; {coverage['recheck']} judged shape{'s' if coverage['recheck'] != 1 else ''} changed since judged — recheck"
     return line

src/scribe/services/shape_ledger.py

@@ -1404,6 +1404,34 @@ def proposal_summary(rows: Iterable[CodeShape], *, top: int = 8) -> dict:
     return {"proposed": proposed, "derive_groups": ranked[:top], "top_canon": top_canon}
 
 
+def derive_new_summary(
+    rows: Iterable[CodeShape], *, since: datetime | None, top: int = 3
+) -> dict:
+    """The arrival-moment drift signal (#2899): derive-grouped rows FIRST
+    SEEN after ``since`` — the previous refresh's stamp, the same one
+    flag_divergence uses. "Since the last refresh, N more copies joined a
+    duplicate family" is the sentence that makes the derive queue a thing
+    you notice on entering, not a thing an audit finds. ``since`` None (a
+    first seed) means nothing is new. Judged rows never count."""
+    if since is None:
+        return {"count": 0, "examples": []}
+    fresh = [
+        r for r in rows
+        if r.proposal_basis == "derive" and r.proposal_group
+        and r.status in _MECHANICAL_TODO and r.vanished_at is None
+        and r.created_at is not None and r.created_at > since
+    ]
+    fresh.sort(key=lambda r: r.created_at, reverse=True)
+    return {
+        "count": len(fresh),
+        "examples": [
+            {"label": ("." if r.kind == "css" else "") + r.symbol,
+             "path": r.path, "group": r.proposal_group}
+            for r in fresh[:top]
+        ],
+    }
+
+
 async def confirm_proposals(
     user_id: int,
     project_id: int,

tests/test_integration_shape_classify.py

@@ -597,6 +597,39 @@ async def test_derive_groups_land_on_rows_and_in_the_summary(seeded):
     assert {r.symbol for r in rows} == {"slug"}                   # 2 files < the name floor
 
 
+@pytest.mark.integration
+async def test_derive_new_names_the_copy_that_joined_a_family_since_the_stamp(seeded):
+    """#2899: the first sync seeds one `slug`; a later sync adds an identical
+    copy. Against the stamp between them, derive_new counts ONLY the
+    newcomer — the drift since the last refresh, not the whole family."""
+    from datetime import datetime, timezone
+
+    from scribe.services.shape_ledger import (
+        apply_derive_groups, derive_new_summary, live_rows,
+    )
+
+    owner, pid = seeded["owner"], seeded["pid"]
+    first = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, first, seen_marker="m1")
+    stamp = datetime.now(timezone.utc)
+    second = _defs(
+        ("a/one.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+        ("a/two.py", "sym", "slug", "def slug(t):", "def slug(t):\n    return t.lower()"),
+    )
+    await sync_repo_shapes(pid, REPO, second, seen_marker="m2")
+    assert await apply_derive_groups(pid) == 2
+
+    rows = await live_rows(pid)
+    out = derive_new_summary(rows, since=stamp)
+    assert out["count"] == 1
+    assert out["examples"][0]["path"] == "a/two.py"
+    assert out["examples"][0]["label"] == "slug"
+    assert out["examples"][0]["group"].startswith("dup:")
+    assert derive_new_summary(rows, since=None)["count"] == 0
+
+
 # --- #2793: the divergence readout against real rows -------------------------
 
 

tests/test_pattern_coverage.py

@@ -276,6 +276,8 @@ async def test_coverage_measures_the_tree_exactly_and_caches(seeded):
     assert coverage["largest_gaps"] == [
         {"dir": "src", "unclassified": 2, "total": 3}
     ]
+    # #2899: a first computation has no previous stamp — nothing is "new".
+    assert coverage["derive_new"] == {"count": 0, "examples": []}
 
     # The walk fed the LEDGER (#2788): every extracted shape has a row, the
     # snippet reference locations are mechanically stamped canonical WITH
@@ -512,6 +514,41 @@ def test_coverage_line_names_the_proposers_standing():
     assert "top canon #2844 ×78" in line and "top copy closed-msg (identical body) ×3 files" in line
 
 
+def test_coverage_line_shows_standing_work_even_with_nothing_unclassified():
+    """#2899: since the scoped bucket a ledger can be fully accounted and
+    still carry derive groups / proposals / divergence — the line names
+    them as `standing:` instead of hiding them behind the todo count, and
+    names the drift since the previous refresh first-copy-first."""
+    from scribe.services.coverage import coverage_line
+
+    base = {
+        "total": 4693, "accounted": 4693, "unclassified": 0,
+        "counts": {"canonical": 37, "instance": 977, "variant": 73, "exempt": 1797, "scoped": 1809},
+        "computed_at": "2026-08-22T00:00:00+00:00", "largest_gaps": [],
+    }
+    quiet = coverage_line(base)
+    assert "unclassified" not in quiet and "standing" not in quiet
+    line = coverage_line({
+        **base,
+        "derive_groups": [{"group": "dup:abc", "label": "log-empty (identical body)", "files": 4}],
+        "derive_new": {"count": 2, "examples": [
+            {"label": ".error-msg", "path": "frontend/src/components/InceptionCard.vue", "group": "dup:9f0"},
+            {"label": ".error-msg", "path": "frontend/src/components/Other.vue", "group": "dup:9f0"},
+        ]},
+        "divergent": 1,
+    })
+    assert "; standing: 1 derive group, +2 new copies since last refresh: .error-msg in " \
+           "frontend/src/components/InceptionCard.vue, 1 DIVERGENT, top copy log-empty (identical body) ×4 files" in line
+    assert "unclassified" not in line
+    # One copy reads singular; with a todo the block keeps its old place.
+    one = coverage_line({**base, "derive_new": {"count": 1, "examples": []}})
+    assert one.endswith("; standing: +1 new copy since last refresh")
+    todo = coverage_line({**base, "unclassified": 3, "accounted": 4690, "proposed": 2,
+                          "derive_new": {"count": 1, "examples": [{"label": "x", "path": "a.py"}]},
+                          "largest_gaps": [{"dir": "src", "unclassified": 3, "total": 9}]})
+    assert "; 3 unclassified (2 proposed, +1 new copy since last refresh: x in a.py), largest: src" in todo
+
+
 def test_coverage_line_names_divergence_and_recheck():
     from scribe.services.coverage import coverage_line
 

tests/test_shape_ledger.py

@@ -317,6 +317,38 @@ def test_derive_groups_copy_before_name_with_floors():
     assert ("i.py", "sym", "one") not in g
 
 
+def test_derive_new_summary_counts_copies_first_seen_since_the_previous_refresh():
+    """#2899: the arrival-moment drift signal — derive-grouped rows created
+    after the previous refresh's stamp, newest first, judged rows and a
+    first seed (since=None) never count."""
+    from datetime import datetime, timedelta, timezone
+
+    from scribe.models.code_shape import CodeShape
+    from scribe.services.shape_ledger import derive_new_summary
+
+    t0 = datetime(2026, 8, 22, 12, 0, tzinfo=timezone.utc)
+
+    def row(path, symbol, at, kind="css", status="scoped", group="dup:abc", basis="derive"):
+        r = CodeShape(project_id=2, repo_key="r", path=path, symbol=symbol, kind=kind,
+                      status=status, proposal_basis=basis, proposal_group=group)
+        r.created_at = at
+        return r
+    rows = [
+        row("v/Old.vue", "error-msg", t0 - timedelta(days=3)),              # before the stamp
+        row("v/InceptionCard.vue", "error-msg", t0 + timedelta(hours=1)),   # new copy
+        row("v/Other.vue", "error-msg", t0 + timedelta(hours=2)),           # newer copy
+        row("v/J.vue", "error-msg", t0 + timedelta(hours=3), status="exempt"),   # judged: never
+        row("s/a.py", "load", t0 + timedelta(hours=1), kind="sym", group=None, basis=None),  # no family
+    ]
+    out = derive_new_summary(rows, since=t0)
+    assert out["count"] == 2
+    assert [e["path"] for e in out["examples"]] == ["v/Other.vue", "v/InceptionCard.vue"]
+    assert out["examples"][0] == {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}
+    assert derive_new_summary(rows, since=None) == {"count": 0, "examples": []}
+    assert derive_new_summary(rows, since=t0, top=1)["examples"] == [
+        {"label": ".error-msg", "path": "v/Other.vue", "group": "dup:abc"}]
+
+
 def test_proposal_summary_ranks_body_identical_groups_first_and_sees_scoped_rows():
     """#2872: dup groups (the real copies) outrank name groups (usually
     convention), wider spread first; #2869: scoped rows are in the readout."""