Phase 2a (lever): expedition retreat semantics split

Phase 2 diagnostics named the InterruptElite bracket as the likely
first lever; tier-walking the lethality probe at the matrix cadence
told a different story.  Phase 1's uniform-0% baseline isn't an
elite-bracket calibration issue at all — every tier reads 0% because
the engine's TimedOut contract was being ignored by every expedition
caller.

combat_engine.go:451 says: "Timeout = retreat, not lethal blow.
Caller treats a timeout loss as 'fight ended, no character death'".
But runHarvestInterrupt / tryPatrolEncounter / resolveCombatRoom all
called abandonZoneRun + retireAllRegionRuns on any !PlayerWon —
ending the expedition outright on a retreat.  The retreat flavor line
("X outlasts you. You retreat from the expedition, wounded but alive")
was already in the code, just stapled to an actual run-abort.

Splits the policy by caller:

  • runHarvestInterrupt   — autopilot daytime interrupt.  TimedOut →
    retreat: threat +5, HP carries over, run continues, harvest slot
    forfeit (no kill / loot).  HP<=0 still ends the run + marks dead.
  • tryPatrolEncounter   — !advance pre-room patrol roll.  Same
    retreat policy: patrols don't gate progress, so retreating from
    one and walking into the next room is the right shape.
  • resolveCombatRoom    — !advance room/elite combat.  Unchanged —
    this path gates room progression; a retreat has nowhere to go, so
    any loss still ends the run.  (Manual zone runs were always
    intended to end here.)

Harness mirrored: daytime interrupt timeout → carry HP + threat bump
+ continue day; night-encounter loss → terminate (mirrors
resolveCombatRoom, since live night encounters defer to !advance).

retreatThreatBump = 5 is the per-retreat threat penalty.  Low enough
not to compound brutally with chained retreats, high enough that 3–4
retreats noticeably walks the threat clock toward Stirring.  Easy to
dial in Phase 3 if zones go off-band.

Phase 1 matrix after the change still reads 0% completion at every
cell — but the encounter counts and survival shape are dramatically
different (T4 underdark 3.6→7.5 encs; T3 underforge trial saw 18
encounters across 10 days where the pre-change run died on day 2/3).
Adds TestExpeditionBalance_Phase2_TierLethality, a tier-walking
companion to the T1/rolls=1 probe, that traces every fight at the
matrix cadence across one zone per tier — the actual Phase 2b lever
work picks from this data, not the old T1-only probe.

The remaining 0% is now legibly driven by tier-disproportionate elite
rosters (Hobgoblin Warchief at T1, Green Hag at T2, Roper/Helmed
Horror higher up) that one-shot or two-shot tier-appropriate
fighters.  Phase 2b's lever shortlist:

  1. Roster gate / SpawnWeight tuning to dilute over-tier elites.
  2. Surprise-nick floor reduction on chained interrupts (carryover
     HP + nick is the death-spiral fingerprint at T1 specifically).
  3. Per-day cadence reduction if 1+2 don't carry T1 to band.

Pre-existing test failures (TestAdv2Scenario_ZoneRunGoblinWarrens,
TestMageSpellbookLineInRender) verified to fail identically on HEAD;
no new test regressions.

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

internal/plugin/dnd_zone_cmd.go

@@ -755,6 +755,12 @@ func (p *AdventurePlugin) resolveCombatRoom(userID id.UserID, run *DungeonRun, z
 		}
 	}
 	if !result.PlayerWon {
+		// resolveCombatRoom gates room progression — a retreat here has
+		// nowhere to go (the elite/room is still blocking the way), so
+		// any loss ends the run. The retreat-continues semantic only
+		// fits the non-gating expedition paths (runHarvestInterrupt,
+		// tryPatrolEncounter); see retreatThreatBump in
+		// dnd_expedition_combat.go.
 		_, _ = applyMoodEvent(run.RunID, MoodEventPlayerDeath)
 		_ = abandonZoneRun(userID)
 		// Timeout loss = retreat; player took wounds but isn't actually