`.tsp._history`: drop orphaned backfill events

- let structured nursery joins own child-task completion
- stop empty provider frames before timestamp endpoint indexing
- cover provider exhaustion and empty frames with bounded tests

Prompt-IO: ai/prompt-io/opencode/20260722T001358Z_16f3cd6f_prompt_io.md

(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))

ai/prompt-io/opencode/20260722T001358Z_16f3cd6f_prompt_io.md

@@ -0,0 +1,36 @@
+---
+model: gpt-5.6-sol
+provider: openai
+service: opencode
+session: ses_0799212ebffe42arY96czXn89F
+timestamp: 2026-07-22T00:13:58Z
+git_ref: 16f3cd6f
+scope: code
+substantive: true
+raw_file: 20260722T001358Z_16f3cd6f_prompt_io.raw.md
+---
+
+## Prompt
+
+Continue the structured backfill phase after the analysis regressions.
+Characterize provider exhaustion and genuinely empty frames, then remove
+completion paths that can hang after child-task exit.
+
+## Response summary
+
+Removed orphan-prone completion events from the structured nursery flow
+and checked empty provider frames before indexing timestamp endpoints.
+Added deterministic timeout-bounded regressions for both exit paths.
+
+## Files changed
+
+- `piker/tsp/_history.py` - structured completion and empty-frame fixes
+- `tests/test_history_backfill.py` - deterministic exit regressions
+- `ai/prompt-io/opencode/20260722T001358Z_16f3cd6f_prompt_io.raw.md`
+  - unedited response record
+- `ai/prompt-io/opencode/20260722T001358Z_16f3cd6f_prompt_io.md`
+  - provenance metadata and response summary
+
+## Human edits
+
+None - generated changes have not yet been edited by the human.

ai/prompt-io/opencode/20260722T001358Z_16f3cd6f_prompt_io.raw.md

@@ -0,0 +1,25 @@
+---
+model: gpt-5.6-sol
+provider: openai
+service: opencode
+timestamp: 2026-07-22T00:13:58Z
+git_ref: 16f3cd6f
+diff_cmd: git diff HEAD~1..HEAD
+---
+
+> `git diff HEAD~1..HEAD -- piker/tsp/_history.py`
+
+Removed redundant completion events whose consumers waited only after
+their owning nurseries had joined. Added empty provider-frame handling
+before timestamp endpoint indexing so provider exhaustion exits cleanly.
+
+> `git diff HEAD~1..HEAD -- tests/test_history_backfill.py`
+
+Added bounded, actor-free regressions for `DataUnavailable` and empty
+provider-frame completion.
+
+Verification generated with the patch:
+
+`timeout -k 5 60 python -m pytest -q tests/test_history_backfill.py`
+
+Result: 2 passed.

piker/tsp/_history.py

@@ -202,12 +202,11 @@ async def maybe_fill_null_segments(
     mkt: MktPair,
     backfill_until_dt: datetime,
 
-    task_status: TaskStatus[trio.Event] = trio.TASK_STATUS_IGNORED,
+    task_status: TaskStatus[None] = trio.TASK_STATUS_IGNORED,
 
 ) -> list[Frame]:
 
-    null_segs_detected = trio.Event()
+    task_status.started()
-    task_status.started(null_segs_detected)
 
     frame: Frame = shm.array
 
@@ -308,7 +307,6 @@ async def maybe_fill_null_segments(
             await tractor.pause()
             raise
 
-    null_segs_detected.set()
     # RECHECK for more null-gaps
     frame: Frame = shm.array
     null_segs: tuple | None = get_null_segs(
@@ -407,15 +405,13 @@ async def start_backfill(
     storage: StorageClient|None = None,
     write_tsdb: bool = True,
 
-    task_status: TaskStatus[tuple] = trio.TASK_STATUS_IGNORED,
+    task_status: TaskStatus[None] = trio.TASK_STATUS_IGNORED,
 
 ) -> int:
 
-        # let caller unblock and deliver latest history frame
+        # Let the caller place storage history while this task
-        # and use to signal that backfilling the shm gap until
+        # continues reverse retrieval in the owning nursery.
-        # the tsdb end is complete!
+        task_status.started()
-        bf_done = trio.Event()
-        task_status.started(bf_done)
 
         # based on the sample step size, maybe load a certain amount history
         update_start_on_prepend: bool = False
@@ -535,6 +531,15 @@ async def start_backfill(
                 #     charge of solving such faults? yes, right?
                 return
 
+            if array.size == 0:
+                log.warning(
+                    f'Provider {mod.name!r} returned an empty frame\n'
+                    f'fqme: {mkt.fqme}\n'
+                    f'timeframe: {timeframe}\n'
+                    f'end_dt: {end_dt_param}\n'
+                )
+                break
+
             time: np.ndarray = array['time']
             assert (
                 time[0]
@@ -800,10 +805,6 @@ async def start_backfill(
         # memory...
         # await sampler_stream.send('broadcast_all')
 
-        # short-circuit (for now)
-        bf_done.set()
-
-
 # NOTE: originally this was used to cope with a tsdb (marketstore)
 # which could not delivery very large frames of history over gRPC
 # (thanks goolag) due to corruption issues.
@@ -1190,7 +1191,7 @@ async def tsdb_backfill(
                 trio.open_nursery() as tn,
             ):
 
-                bf_done: trio.Event = await tn.start(
+                await tn.start(
                     partial(
                         start_backfill,
                         get_hist=get_hist,
@@ -1210,8 +1211,6 @@ async def tsdb_backfill(
                         write_tsdb=True,
                     )
                 )
-                nulls_detected: trio.Event|None = None
-
                 if last_tsdb_dt is not None:
 
                     # calc the index from which the tsdb data should be
@@ -1288,7 +1287,7 @@ async def tsdb_backfill(
                     #    work PREVENTAVELY instead?
                     # -[ ] fill in non-zero epoch time values ALWAYS!
                     # await maybe_fill_null_segments(
-                    nulls_detected: trio.Event = await tn.start(partial(
+                    await tn.start(partial(
                         maybe_fill_null_segments,
 
                         shm=shm,
@@ -1301,11 +1300,6 @@ async def tsdb_backfill(
 
             # 2nd nursery END
 
-            # TODO: who would want to?
-            if nulls_detected:
-                await nulls_detected.wait()
-
-            await bf_done.wait()
         # TODO: maybe start history anal and load missing "history
         # gaps" via backend..
 

tests/test_history_backfill.py

@@ -0,0 +1,69 @@
+'''
+Deterministic history-backfill regressions.
+
+'''
+from functools import partial
+from types import SimpleNamespace
+
+import numpy as np
+from pendulum import datetime
+import trio
+
+from piker.brokers import DataUnavailable
+from piker.data._source import def_iohlcv_fields
+from piker.tsp._history import start_backfill
+
+
+def run_exhausted_backfill(get_hist) -> None:
+    '''
+    Run a provider-exhaustion case without actor services.
+
+    '''
+    async def main() -> None:
+        with trio.fail_after(0.5):
+            async with trio.open_nursery() as nursery:
+                await nursery.start(partial(
+                    start_backfill,
+                    get_hist=get_hist,
+                    def_frame_duration=None,
+                    mod=SimpleNamespace(name='fake'),
+                    mkt=SimpleNamespace(fqme='x.fake'),
+                    shm=object(),
+                    timeframe=60,
+                    backfill_from_shm_index=100,
+                    backfill_from_dt=datetime(2026, 1, 2),
+                    sampler_stream=object(),
+                    backfill_until_dt=datetime(2026, 1, 1),
+                    storage=None,
+                    write_tsdb=False,
+                ))
+
+    trio.run(main)
+
+
+def test_data_unavailable_completes() -> None:
+    '''
+    Provider exhaustion exits without orphaned completion waits.
+
+    '''
+    async def get_hist(*args, **kwargs):
+        raise DataUnavailable('history exhausted')
+
+    run_exhausted_backfill(get_hist)
+
+
+def test_empty_frame_completes() -> None:
+    '''
+    An empty provider frame is checked before endpoint indexing.
+
+    '''
+    frame = np.empty(
+        0,
+        dtype=np.dtype(def_iohlcv_fields),
+    )
+
+    async def get_hist(*args, **kwargs):
+        end_dt = kwargs['end_dt']
+        return frame, end_dt, end_dt
+
+    run_exhausted_backfill(get_hist)