feat(legacy-meter): scale retirement quiet period to call volume

A clean review window only proves an interface was silent for that window.
For a heavily used interface that is weak evidence -- an infrequent caller
can fall outside the window entirely, so the interface reads as retirable
while still having consumers.

_retirement_state now also requires silence since last_seen_at, scaled by
all-time volume (RETIREMENT_QUIET_LADDER): 7d under 100 calls, 30d under
10k, 60d above. Existing guards (retired / manual hold / replacement ref /
replacement verified / in-window traffic) still take precedence.

On the 2026-08-20 capture this makes 15 of 19 legacy interfaces retirable
and holds 4: the three six-figure /workstreams/ read paths, and
GET /tasks/?workstream_id which still has live traffic.

Unblocks the bulk of Wave E2 in the cutover slice plan. 7 new tests.

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

api/services/legacy_meter.py

@@ -305,7 +305,13 @@ def _summarize_interface(
     ]
     window = _counters(window_buckets)
     last_seen = max((bucket.last_seen_at for bucket in buckets), default=None)
-    retirement_candidate, reason = _retirement_state(interface, window.calls)
+    retirement_candidate, reason = _retirement_state(
+        interface,
+        window.calls,
+        all_time_calls=all_time.calls,
+        last_seen_at=last_seen,
+        window_end=window_end,
+    )
     return LegacyInterfaceSummary(
         interface=LegacyInterfaceRead.model_validate(interface),
         all_time=all_time,
@@ -340,7 +346,34 @@ def _bucket_counts(buckets: list[LegacyInterfaceUsageBucket], bucket_kind: str)
     return counts
 
 
-def _retirement_state(interface: LegacyInterface, window_calls: int) -> tuple[bool, str]:
+# Minimum quiet period before an interface may be retired, scaled to how much
+# traffic it ever carried. A review window only proves the interface was silent
+# for that window; for a high-volume interface that is weak evidence, since a
+# monthly or quarterly caller can easily fall outside it. Thresholds are
+# (all-time calls, minimum days since last_seen_at).
+RETIREMENT_QUIET_LADDER: tuple[tuple[int, int], ...] = (
+    (10_000, 60),
+    (100, 30),
+    (1, 7),
+)
+
+
+def _required_quiet_days(all_time_calls: int) -> int:
+    """Days of silence required before retirement, by all-time call volume."""
+    for threshold, days in RETIREMENT_QUIET_LADDER:
+        if all_time_calls >= threshold:
+            return days
+    return 0
+
+
+def _retirement_state(
+    interface: LegacyInterface,
+    window_calls: int,
+    *,
+    all_time_calls: int = 0,
+    last_seen_at: datetime | None = None,
+    window_end: datetime | None = None,
+) -> tuple[bool, str]:
     if interface.status == "retired":
         return False, "already retired"
     if interface.manual_hold:
@@ -351,6 +384,19 @@ def _retirement_state(interface: LegacyInterface, window_calls: int) -> tuple[bo
         return False, "replacement not verified"
     if window_calls > 0:
         return False, f"{window_calls} call(s) in review window"
+
+    required_days = _required_quiet_days(all_time_calls)
+    if required_days and last_seen_at is not None and window_end is not None:
+        quiet_days = (window_end - _ensure_datetime(last_seen_at)).days
+        if quiet_days < required_days:
+            return False, (
+                f"quiet {quiet_days}d of {required_days}d required "
+                f"for {all_time_calls} all-time call(s)"
+            )
+        return True, (
+            f"no usage in review window; quiet {quiet_days}d "
+            f"(>= {required_days}d required for {all_time_calls} all-time call(s))"
+        )
     return True, "no measured usage in review window"
 
 

docs/retirement-cutover-slice-plan.md

@@ -213,21 +213,43 @@ retirement evidence. Corrected capture:
 `docs/evidence/legacy-meter-weekly-review-20260820.json` — 18 candidates of 20
 interfaces, `GET /tasks/?workstream_id` correctly excluded.
 
-**Still open — E2 remains gated.** A 7-day window is not sufficient for
+**Candidate rule tightened (2026-08-20).** `_retirement_state` now requires a
-high-volume interfaces, and two false positives survive it:
+quiet period scaled to all-time call volume, because a clean window only proves
+silence for that window — for a heavily used interface an infrequent caller can
+fall outside it entirely. `RETIREMENT_QUIET_LADDER` in
+`api/services/legacy_meter.py`:
 
-- `GET /progress/?workstream_id` — last seen 2026-08-12T08:55Z, roughly 14 hours
+| All-time calls | Days since `last_seen_at` required |
-  before the window opened
+| --- | --- |
-- `GET /workstreams/` — last seen 2026-08-10, 9 days quiet, 144 086 all-time calls
+| 0 | none — never used |
+| 1 – 99 | 7 |
+| 100 – 9 999 | 30 |
+| 10 000+ | 60 |
 
-`last_seen_at` is unbounded by the window and is the stronger signal; the
+Applied to the 2026-08-20 capture this splits the 19 legacy interfaces cleanly:
-candidate rule currently ignores it. Before E2 proceeds, the rule should require
-a minimum quiet period scaled to call volume — an interface with six figures of
-traffic needs materially more than seven silent days. That is a service-side
-change in `api/services/legacy_meter.py` and belongs to T05, not here.
 
-Everything else on the list was last seen 2026-07-31 or earlier, most in early
+**15 retirable** — all four `workstream` MCP tools, the `state://` resource, and
-July, so the bulk of E2 is well-evidenced once the rule is tightened.
+the low-volume REST aliases, plus `PATCH /workstreams/{id}` (571 calls, quiet
+42d), `POST /workstreams/` (824, quiet 42d) and
+`POST /workstreams/{id}/dependencies/` (4 971, quiet 49d).
+
+**4 held:**
+
+| Interface | All-time calls | Reason |
+| --- | --- | --- |
+| `GET /tasks/?workstream_id` | 595 | traffic inside the window |
+| `GET /workstreams/` | 144 086 | quiet 9d of 60d |
+| `GET /workstreams/{id}` | 511 406 | quiet 19d of 60d |
+| `GET /workstreams/{id}/dependencies/` | 255 865 | quiet 42d of 60d |
+
+E2 can therefore proceed for the 15, which is the bulk of the slice. The four
+held are the three six-figure read paths and the one with live traffic — exactly
+the set where a false retirement would hurt most. They clear on their own as the
+quiet counter runs, provided no new traffic arrives; the earliest,
+`GET /workstreams/{id}/dependencies/`, needs 18 more silent days.
+
+Re-check before executing E2: the ladder is evaluated at review time, so a
+capture older than the retirement decision is not evidence for it.
 
 ## Keep — 43 items
 

tests/test_legacy_meter.py

@@ -486,3 +486,137 @@ class TestWorkplanAliasesAndLegacyMeter:
         assert items["rest_api:DELETE /workstreams/{workstream_id}/dependencies/{dep_id}"]["window"]["components"] == {
             "old-dep-archiver": 1
         }
+
+
+# --- retirement quiet-period ladder (STATE-WP-0079-T05) ---------------------
+#
+# A clean review window only proves silence for that window. For an interface
+# that carried heavy traffic, that is weak evidence: an infrequent caller can
+# fall outside the window entirely. The ladder requires silence proportional to
+# all-time volume before an interface becomes a retirement candidate.
+
+
+def _iface(**kw):
+    from types import SimpleNamespace
+
+    defaults = dict(
+        status="legacy",
+        manual_hold=False,
+        hold_reason=None,
+        replacement_ref="replacement",
+        replacement_verified=True,
+    )
+    defaults.update(kw)
+    return SimpleNamespace(**defaults)
+
+
+def test_required_quiet_days_scales_with_volume():
+    from api.services.legacy_meter import _required_quiet_days
+
+    assert _required_quiet_days(0) == 0
+    assert _required_quiet_days(1) == 7
+    assert _required_quiet_days(99) == 7
+    assert _required_quiet_days(100) == 30
+    assert _required_quiet_days(9_999) == 30
+    assert _required_quiet_days(10_000) == 60
+    assert _required_quiet_days(511_406) == 60
+
+
+def test_high_volume_interface_held_until_quiet_period_elapses():
+    """A six-figure interface quiet for 9 days is not yet retirable."""
+    from api.services.legacy_meter import _retirement_state
+
+    window_end = datetime(2026, 8, 20, tzinfo=timezone.utc)
+    candidate, reason = _retirement_state(
+        _iface(),
+        0,
+        all_time_calls=144_086,
+        last_seen_at=datetime(2026, 8, 11, tzinfo=timezone.utc),
+        window_end=window_end,
+    )
+    assert candidate is False
+    assert "9d of 60d required" in reason
+
+
+def test_high_volume_interface_retirable_once_quiet_long_enough():
+    from api.services.legacy_meter import _retirement_state
+
+    window_end = datetime(2026, 8, 20, tzinfo=timezone.utc)
+    candidate, reason = _retirement_state(
+        _iface(),
+        0,
+        all_time_calls=144_086,
+        last_seen_at=datetime(2026, 5, 1, tzinfo=timezone.utc),
+        window_end=window_end,
+    )
+    assert candidate is True
+    assert "60d required" in reason
+
+
+def test_low_volume_interface_uses_short_quiet_period():
+    from api.services.legacy_meter import _retirement_state
+
+    window_end = datetime(2026, 8, 20, tzinfo=timezone.utc)
+    candidate, _ = _retirement_state(
+        _iface(),
+        0,
+        all_time_calls=2,
+        last_seen_at=datetime(2026, 8, 12, tzinfo=timezone.utc),
+        window_end=window_end,
+    )
+    assert candidate is True
+
+
+def test_never_used_interface_needs_no_quiet_period():
+    from api.services.legacy_meter import _retirement_state
+
+    candidate, reason = _retirement_state(
+        _iface(),
+        0,
+        all_time_calls=0,
+        last_seen_at=None,
+        window_end=datetime(2026, 8, 20, tzinfo=timezone.utc),
+    )
+    assert candidate is True
+    assert reason == "no measured usage in review window"
+
+
+def test_in_window_traffic_still_wins_over_quiet_ladder():
+    """Traffic inside the window blocks retirement regardless of volume."""
+    from api.services.legacy_meter import _retirement_state
+
+    candidate, reason = _retirement_state(
+        _iface(),
+        3,
+        all_time_calls=5,
+        last_seen_at=datetime(2026, 8, 19, tzinfo=timezone.utc),
+        window_end=datetime(2026, 8, 20, tzinfo=timezone.utc),
+    )
+    assert candidate is False
+    assert "3 call(s) in review window" in reason
+
+
+def test_existing_guards_precede_quiet_ladder():
+    from api.services.legacy_meter import _retirement_state
+
+    window_end = datetime(2026, 8, 20, tzinfo=timezone.utc)
+    long_quiet = dict(
+        all_time_calls=1,
+        last_seen_at=datetime(2026, 1, 1, tzinfo=timezone.utc),
+        window_end=window_end,
+    )
+    assert _retirement_state(_iface(status="retired"), 0, **long_quiet) == (
+        False,
+        "already retired",
+    )
+    assert _retirement_state(
+        _iface(manual_hold=True, hold_reason="pinned"), 0, **long_quiet
+    ) == (False, "pinned")
+    assert _retirement_state(_iface(replacement_ref="  "), 0, **long_quiet) == (
+        False,
+        "missing replacement reference",
+    )
+    assert _retirement_state(_iface(replacement_verified=False), 0, **long_quiet) == (
+        False,
+        "replacement not verified",
+    )

workplans/STATE-WP-0079-retirement-strangler.md

@@ -141,11 +141,19 @@ live callers, including `GET /tasks/?workstream_id` (seen 2026-08-18).
 Script default corrected to `days=7`; corrected capture
 `docs/evidence/legacy-meter-weekly-review-20260820.json`.
 
-**Remaining work for this task:** the candidate rule in
+**Candidate rule tightened (2026-08-20):** `_retirement_state` now requires a
-`api/services/legacy_meter.py` keys only on in-window calls and ignores
+quiet period scaled to all-time call volume (`RETIREMENT_QUIET_LADDER`: 7d under
-`last_seen_at`, so `GET /workstreams/` (144 086 all-time calls, quiet 9 days)
+100 calls, 30d under 10 000, 60d above). On the 2026-08-20 capture this makes 15
-still reports as a candidate. Require a minimum quiet period scaled to call
+of 19 legacy interfaces retirable — all `workstream` MCP tools, the `state://`
-volume before retiring. See `docs/retirement-cutover-slice-plan.md` § E2.
+resource, and the low-volume REST aliases — while holding the three six-figure
+read paths (`GET /workstreams/`, `GET /workstreams/{id}`,
+`GET /workstreams/{id}/dependencies/`) and `GET /tasks/?workstream_id`, which
+still has live traffic. Covered by 7 new tests in `tests/test_legacy_meter.py`.
+
+**Remaining work for this task:** execute the retirement of the 15 evidenced
+interfaces, then re-review the 4 held ones as their quiet counters run. The
+ladder is evaluated at review time, so re-capture before deciding. See
+`docs/retirement-cutover-slice-plan.md` § E2.
 
 ## Stabilization window and archive prep