From a516c2b2b69328493956cc8d28e94febd2c3beee Mon Sep 17 00:00:00 2001
From: Rene De Ren <zn375ix3@gmail.com>
Date: Wed, 6 May 2026 17:17:58 +0200
Subject: [PATCH] MeasurementContainer.get: strict-resolve explicit
 .child(name)
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A read chain `.child(name).getCurrentValue()` previously fell through
silently to the implicit-default child or the first available sibling
when the named child did not exist. Caller asked for X, got Y, no
warning. Surfaced via pumpingStation spillPrev: a fresh basin's
.child('overflow').getCurrentValue() returned the value of
'manual-qout' (the only existing child at that position).

Split the resolution into two strictness levels:
  _currentChildId (per-chain .child(name)) → STRICT, missing = null.
  this.childId    (persistent setChildId)  → HINT, falls back to
                                              'default' then first.

The persistent path is what registered children (rotatingMachine etc.)
rely on: they write under composed ids ('up-<id>') but expect reads
without explicit .child() to still resolve.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 src/measurements/MeasurementContainer.js | 32 ++++++++++++++++++------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/src/measurements/MeasurementContainer.js b/src/measurements/MeasurementContainer.js
index 9ceb8af..5788f3d 100644
--- a/src/measurements/MeasurementContainer.js
+++ b/src/measurements/MeasurementContainer.js
@@ -425,16 +425,34 @@ class MeasurementContainer {
       // Legacy single measurement
       if (posBucket?.getCurrentValue) return posBucket;
 
-      // Child-aware: pick requested child, otherwise fall back to default, otherwise first available
+      // Child-aware lookup. Two separate sources of "child-id" on the
+      // container, with DIFFERENT strictness:
+      //
+      //   _currentChildId : transient, set by .child(name) inside a chain.
+      //                     Explicit per-call. STRICT — if the named child
+      //                     does not exist, return null. Silent fall-through
+      //                     to a sibling would mask a missing-stream read
+      //                     as a wrong-stream read (see pumpingStation
+      //                     spillPrev bug, 2026-05-06).
+      //
+      //   this.childId    : persistent, set by setChildId(id). HINT only —
+      //                     try it first, then fall back to 'default' then
+      //                     first available. Containers registered with a
+      //                     persistent id (rotatingMachine, etc.) write
+      //                     under composed child ids (e.g. 'up-<id>') that
+      //                     don't equal the persistent id, and reads must
+      //                     still resolve to those writes.
       if (posBucket && typeof posBucket === 'object') {
-        const requestedKey = this._currentChildId || this.childId;
         const keys = Object.keys(posBucket);
         if (!keys.length) return null;
-        const measurement =
-          (requestedKey && posBucket[requestedKey]) ||
-          posBucket.default ||
-          posBucket[keys[0]];
-        return measurement || null;
+
+        if (this._currentChildId) {
+          return posBucket[this._currentChildId] || null;
+        }
+        return (this.childId && posBucket[this.childId]) ||
+               posBucket.default ||
+               posBucket[keys[0]] ||
+               null;
       }
 
       return null;