Adv 2.0 D&D Phase 12 E2c: Siege Mode effects + threat-70 warning

§8.3 siege economics:
- applyDailyBurn now takes an explicit siege flag and enforces a 2× floor
  on supply burn even when HarshMod is below 2 (tier-1 zones still get
  starved out per spec).
- currentBurn mirrors the same precedence so status/briefing readouts
  stay consistent.
- Briefing rollover passes e.SiegeMode through, decoupling siege from
  the harsh-conditions composite.

§8.3 threat-70 warning: applyDailyThreatDrift emits a one-time
appendApproachingSiegeLog when the level crosses 70 (prevLevel<70 and
new level≥70). Pulls from a new flavor.ThreatClockApproachingSiege pool
seeded with the spec's verbatim warning beat plus two voice-matched
alternates.

Other siege effects (boss +20 HP / Legendary Resistance, cleared-room
respawn, no-short-rest enforcement) stay deferred to the combat-link
phase — ThreatBandInfo already exposes the flags that engine will read.

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

internal/flavor/twinbee_expedition_flavor.go

@@ -155,6 +155,16 @@ var ThreatClockSiege = []string{
 	"Siege Mode. TwinBee delivers this without decoration because decoration would be dishonest. The dungeon is fully active, fully aware, and fully committed to ending this expedition. So is TwinBee — to ending it on your terms, not theirs. What happens next is a race. TwinBee is already running.",
 }
 
+// ThreatClockApproachingSiege fires once when the threat clock crosses 70 —
+// the spec's "begin warning" line (§8.3). Distinct from the Hostile-band
+// flavor because this is the dungeon-design moment of telling the player
+// they're past the point where stealth is recoverable.
+var ThreatClockApproachingSiege = []string{
+	"They know you're here. Not a suspicion anymore. A certainty. The question now is whether you finish before they organize. TwinBee says this clearly so it doesn't have to be said again.",
+	"Threat at seventy. TwinBee marks this on the internal ledger and underlines it. The window for quiet operations has closed. The window for finishing is still open — narrower, but open. TwinBee suggests using it.",
+	"The dungeon's posture has shifted from 'searching' to 'hunting.' TwinBee tracks the difference precisely: before, they were looking for evidence; now they are looking for you. The plan, accordingly, simplifies. Finish or extract. Middle paths have closed.",
+}
+
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