fix(run): address round-2 gadfly nits (max(), drop dead soft fallback, decouple doc)

All low-severity follow-ups on the critic-deadline change:
- hardCap uses max(CriticAbsoluteMax, maxRuntime) instead of a nested if (723193a7).
- Drop the now-dead 90s soft-trigger fallback + its bare literal: the sole caller
  passes the resolved MaxRuntime (>0), and Run's unsupervised-run failsafe bounds
  even an impossible 0 (8d377051, 2f86bf58).
- Decouple the kernel doc from a named downstream convar ("a 6h host convar")
  (730c67fc).

Graded false-positive: agent.go BackstopMultiplier validation (handled in the host;
not in this diff), the 24h default "magic number" (matches every withFallbacks
default), and the defer-in-conditional pattern (idiomatic). Kept: the thorough
two-tier comment (this logic regressed once) and the rare-path nested timer.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jo75sqmeVPgFUWZQBn179X

run/critic.go

@@ -44,18 +44,15 @@ func (e *Executor) criticOwnsDeadline(ra RunnableAgent) bool {
 // is the soft wake (mort's two-tier semantics — the critic first reviews once the
 // run exceeds its nominal budget, and its backstop = softTrigger × multiplier).
 // The caller (Run) always passes the resolved MaxRuntime, which withFallbacks
-// guarantees is > 0; the 90s floor below is purely a defensive guard for a
-// hypothetical caller that passes a non-positive value.
+// guarantees is > 0, so no fallback is needed here. (A non-positive soft would make
+// the host Monitor return no handle, and Run's unsupervised-run failsafe then bounds
+// the run at MaxRuntime — so even that impossible case stays bounded.)
 func (e *Executor) startCritic(runCtx context.Context, cancelCause context.CancelCauseFunc, ra RunnableAgent, info RunInfo, softTrigger time.Duration) (*criticBinding, func()) {
 	noop := func() {}
 	if !e.criticOwnsDeadline(ra) {
 		return nil, noop
 	}
-	soft := softTrigger
-	if soft <= 0 {
-		soft = 90 * time.Second // defensive only; the sole caller passes MaxRuntime (>0)
-	}
-	h := e.cfg.Ports.Critic.Monitor(runCtx, info, soft)
+	h := e.cfg.Ports.Critic.Monitor(runCtx, info, softTrigger)
 	if h == nil {
 		return nil, noop
 	}