fix(orchestrator): let a failed Board Program exploration retry (#706)

`_board_dispatched` is an in-memory, never-expiring set of
(agent_slug, task_id). The solo exploration dispatchers consulted it, so an
exploration whose propose verb rejected was never retried for the life of the
process — Periscope, Sentinel, Scales and Barfly each spawned once on
2026-07-25, failed, and sat PENDING until the stack restarted.

The guard was written for the two-reviewer board REVIEW pass, where it is
correct: a reviewer has no verb to advance the task, so a respawn can only
loop. An explorer is the opposite — `propose_*` is exactly such a verb, so a
respawn can and should advance it.

Drop it from the 15 `_dispatch_*_exploration` functions. Bounding falls to
`_pm_respawn_should_gate`, which is what actually bounds a loop: DB-persisted,
reset by a status change, and cooled down so a deploy that fixes the cause
lets the work resume. `_dispatch_board_reviewer` keeps the set (its
`_board_review_complete` reads it as a has-run signal) as does vault
curation (same-process race guard behind its own durable marker).

The 14 `*_dispatch_is_one_shot` tests asserted the old contract on the false
rationale that board roles have no progression verb; they now assert a second
tick re-attempts.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/runtime/test_roadmap_dispatch.py

@@ -57,9 +57,15 @@ async def test_roadmap_dispatch_spawns_only_product_owner() -> None:
 
 
 @pytest.mark.asyncio
-async def test_roadmap_dispatch_is_one_shot() -> None:
-    """Re-ticking a still-unauthored, still-pending cycle must NOT respawn —
-    board roles have no progression verb, so a respawn would just loop."""
+async def test_roadmap_dispatch_retries_until_breaker() -> None:
+    """A failed exploration must be retried, not abandoned.
+
+    The explorer has a progression verb (``propose_*``), so a respawn CAN
+    advance the task — unlike the two-reviewer review pass this guard was
+    originally written for. Bounding belongs to
+    ``_pm_respawn_should_gate`` (DB-persisted, reset by a status change),
+    not to a never-expiring in-memory set.
+    """
     orch = _make_orch()
     task = _roadmap_task()
     with (
@@ -70,7 +76,10 @@ async def test_roadmap_dispatch_is_one_shot() -> None:
         await orch._dispatch_roadmap_exploration(task)
         await orch._dispatch_roadmap_exploration(task)
 
-    spawn.assert_awaited_once()
+    ticks = 2
+    assert spawn.await_count == ticks, (
+        "a second tick must re-attempt a failed exploration"
+    )
 
 
 @pytest.mark.asyncio