Revert "feat(policy): cold-D bonus to break overlap-pinning death spiral"

Implementation jumped ahead of design. The cold-D bonus is one of
several candidates for the overlap-pinning fix (others: load-floor
bonus, idle-D bonus, capacity-aware overlap discount, pre-warming
boilerplate). Need to evaluate the design space first, including
whether a single bonus is even the right shape vs a separate term
in the lex score, before committing to a specific knob.

This reverts commit 786cbb8 cleanly (forensic docs in bf4da28 and
7f2ebf3 are kept since they record observations, not designs).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/agentic_pd_hybrid/replay.py

@@ -111,10 +111,6 @@ class ReplayConfig:
     # KvAwarePolicy skips that D for the session (forcing migration). Default 3.
     # Set 0 to disable. See REFACTOR_PLAN_V1 §6.2.
     kvcache_migration_reject_threshold: int = 3
-    # Cold-D bonus: synthetic boost to lex-score position 0 for any D worker
-    # that has never been assigned a session yet, applied only when the request
-    # has no sticky preference. 0 disables. See docs/E1_E2_RESULTS_ZH.md §5d.
-    kvcache_cold_d_bonus: int = 0
     structural_log_dir: Path | None = None
 
 
@@ -202,7 +198,6 @@ async def replay_trace(config: ReplayConfig) -> list[RequestMetrics]:
     policy = create_policy(
         config.policy_name,
         migration_reject_threshold=config.kvcache_migration_reject_threshold,
-        cold_d_bonus=config.kvcache_cold_d_bonus,
     )
     state = RoutingState.create(config.topology)
     state_lock = asyncio.Lock()