.tsp._history: add gap detection in backfill loop

Add frame-gap detection when `frame_last_dt < end_dt_param` to
warn about potential venue closures or missing data during the
backfill loop in `start_backfill()`.

Deats,
- add `frame_last_dt < end_dt_param` check after frame recv
- log warnings with EST-converted timestamps for clarity
- add `await tractor.pause()` for REPL-investigation on gaps
- add TODO comment about venue closure hour checking
- capture `_until_was_none` walrus var for null-check clarity
- add `last_time` assertion for `time[-1] == next_end_dt`
- rename `_daterr` to `nodata` with `_nodata` capture

Also,
- import `pendulum.timezone` and create `est` tz instance
- change `get_logger()` import from `.data._util` to `.log`
- add parens around `(next_prepend_index - ln) < 0` check

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/tsp/_history.py

@@ -49,6 +49,7 @@ from pendulum import (
     Duration,
     duration as mk_duration,
     from_timestamp,
+    timezone,
 )
 import numpy as np
 import polars as pl
@@ -57,9 +58,7 @@ from piker.brokers import NoData
 from piker.accounting import (
     MktPair,
 )
-from piker.data._util import (
+from piker.log import get_logger
-    log,
-)
 from ..data._sharedmem import (
     maybe_open_shm_array,
     ShmArray,
@@ -97,6 +96,9 @@ if TYPE_CHECKING:
     # from .feed import _FeedsBus
 
 
+log = get_logger()
+
+
 # `ShmArray` buffer sizing configuration:
 _mins_in_day = int(60 * 24)
 # how much is probably dependent on lifestyle
@@ -401,7 +403,9 @@ async def start_backfill(
 
         # based on the sample step size, maybe load a certain amount history
         update_start_on_prepend: bool = False
-        if backfill_until_dt is None:
+        if (
+            _until_was_none := (backfill_until_dt is None)
+        ):
 
             # TODO: per-provider default history-durations?
             # -[ ] inside the `open_history_client()` config allow
@@ -435,6 +439,8 @@ async def start_backfill(
         last_start_dt: datetime = backfill_from_dt
         next_prepend_index: int = backfill_from_shm_index
 
+        est = timezone('EST')
+
         while last_start_dt > backfill_until_dt:
             log.info(
                 f'Requesting {timeframe}s frame:\n'
@@ -448,9 +454,10 @@ async def start_backfill(
                     next_end_dt,
                 ) = await get_hist(
                     timeframe,
-                    end_dt=last_start_dt,
+                    end_dt=(end_dt_param := last_start_dt),
                 )
-            except NoData as _daterr:
+            except NoData as nodata:
+                _nodata = nodata
                 orig_last_start_dt: datetime = last_start_dt
                 gap_report: str = (
                     f'EMPTY FRAME for `end_dt: {last_start_dt}`?\n'
@@ -518,8 +525,32 @@ async def start_backfill(
                 ==
                 next_start_dt.timestamp()
             )
+            assert (
+                (last_time := time[-1])
+                ==
+                next_end_dt.timestamp()
+            )
 
-            assert time[-1] == next_end_dt.timestamp()
+            frame_last_dt = from_timestamp(last_time)
+            if (
+                frame_last_dt.add(seconds=timeframe)
+                <
+                end_dt_param
+            ):
+                est_frame_last_dt = est.convert(frame_last_dt)
+                est_end_dt_param = est.convert(end_dt_param)
+                log.warning(
+                    f'Provider frame ending BEFORE requested end_dt={end_dt_param} ??\n'
+                    f'frame_last_dt (EST): {est_frame_last_dt!r}\n'
+                    f'end_dt_param (EST): {est_end_dt_param!r}\n'
+                    f'\n'
+                    f'Likely contains,\n'
+                    f'- a venue closure.\n'
+                    f'- (maybe?) missing data ?\n'
+                )
+                # ?TODO, check against venue closure hours
+                # if/when provided by backend?
+                await tractor.pause()
 
             expected_dur: Interval = (
                 last_start_dt.subtract(
@@ -581,10 +612,11 @@ async def start_backfill(
                     '0 BARS TO PUSH after diff!?\n'
                     f'{next_start_dt} -> {last_start_dt}'
                 )
+                await tractor.pause()
 
             # Check if we're about to exceed buffer capacity BEFORE
             # attempting the push
-            if next_prepend_index - ln < 0:
+            if (next_prepend_index - ln) < 0:
                 log.warning(
                     f'Backfill would exceed buffer capacity!\n'
                     f'next_prepend_index: {next_prepend_index}\n'
@@ -655,7 +687,7 @@ async def start_backfill(
                     },
                 })
 
-                # can't push the entire frame? so
+                # XXX, can't push the entire frame? so
                 # push only the amount that can fit..
                 break
 
@@ -715,8 +747,8 @@ async def start_backfill(
                 ) = dedupe(df)
                 if diff:
                     log.warning(
-                        f'Found {diff} duplicates in tsdb, '
+                        f'Found {diff!r} duplicates in tsdb! '
-                        f'overwriting with deduped data\n'
+                        f'=> Overwriting with `deduped` data !! <=\n'
                     )
                     await storage.write_ohlcv(
                         col_sym_key,