docs: why-gates-are-code haelt fest, dass ein Gate in Code auch erreichbar sein muss

Files changed:
- docs/why-gates-are-code.md

docs/why-gates-are-code.md

@@ -51,6 +51,28 @@ The Iteration Budget Gate asks a fourth kind of question - not "is this instance
 itself (call count, repeated identical calls), not from anything about the content of any one
 call.
 
+## A gate in code still has to be reachable
+
+Code beats prose for the reason above, but on its own it buys less than it looks like: a check
+that runs on every call is only as good as the thing it counts under. The Iteration Budget Gate
+scopes its counter to a session, and "session" was approximated by the parent process id whenever
+nothing set an explicit one. On a harness that runs every tool call in a freshly initialised
+shell, that approximation hands out a new session per call - so a traced run of thirty-three calls
+arrived as twenty-one sessions of one to three calls each, the ceiling of sixty was never
+approached, and the loop-breaker's window never held three calls at once to compare. The gate ran
+on every one of those calls, exactly as written, and refused nothing.
+
+That failure has no symptom of its own. A gate that fires announces that it exists; a gate that
+*cannot* fire looks identical to a gate nobody happened to need - the same clean runs, the same
+silence - and what finally told the two apart was reading a trace for an unrelated reason. So
+there is a third property to keep alongside living in code and carrying measured numbers: each
+gate has to leave evidence that it can still fire. The three that clear by token or by a
+deliberate edit have it by construction, because clearing one is a visible event in somebody's
+terminal. The budget gate, whose ordinary outcome is silence, is the one that had to be given
+it - which is why its session id now carries where it came from, into both the trace and
+`budget status`, so a session's own record answers the question instead of an investigation
+having to.
+
 ## Numbers that come from measurement, not intuition
 
 The iteration ceiling didn't start where it sits now. It used to run 15-25, borrowed from a