style: palette swatch → (domain-hue redesign 2026-05-21)

Sidebar swatch now follows function family rather than S88 level, so the
palette is visually identifiable instead of monochromatically blue. Editor-group
rectangles in flow.json still follow S88 — only the registerType color changed.
Full table + rationale: superproject .claude/rules/node-red-flow-layout.md §10.0
and .claude/refactor/OPEN_QUESTIONS.md (2026-05-21 entry).

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

CLAUDE.md

@@ -21,3 +21,20 @@ Key points for this node:
 - Stack same-level siblings vertically.
 - Parent/children sit on adjacent lanes (children one lane left, parent one lane right).
 - Wrap in a Node-RED group box coloured `#50a8d9` (Unit).
+
+## Folder & File Layout
+
+Every per-node file MUST use the folder name (`settler`) **exactly**, case-sensitive. Full rule: [`.claude/rules/node-architecture.md`](https://gitea.wbd-rd.nl/RnD/EVOLV/src/branch/development/.claude/rules/node-architecture.md) in the EVOLV superproject.
+
+| Path | Required name |
+|---|---|
+| Entry file | `settler.js` |
+| Editor HTML | `settler.html` |
+| Node adapter | `src/nodeClass.js` |
+| Domain logic | `src/specificClass.js` |
+| Editor JS modules | `src/editor/*.js` (extract when inline editor JS exceeds ~50 lines) |
+| Tests | `test/{basic,integration,edge}/*.test.js` |
+| Example flows | `examples/*.flow.json` |
+
+
+When adding new files, read the rule above first to avoid drift.

CONTRACT.md

@@ -8,10 +8,9 @@ Hand-maintained for Phase 6; the `## Inputs` table is generated from
 | Canonical | Aliases (deprecated) | Payload | Effect |
 |---|---|---|---|
 | `data.influent` | `influent`, `setInfluent` | `{ F: number, C: number[13] }` — either field optional | Replaces influent flow and/or the 13-species concentration vector. Triggers `output-changed`, re-emits the 3-stream Fluent envelope. |
+| `child.register` | `registerChild` | `string` — the child node's Node-RED id | Resolves the child via `RED.nodes.getNode` and registers it through `childRegistrationUtils` at the supplied `msg.positionVsParent`. |
 
 Aliases log a one-time deprecation warning the first time they fire.
-Plumbing topics (`child.register`) are handled by the BaseNodeAdapter and
-not listed here.
 
 ## Outputs
 

package.json

@@ -16,7 +16,10 @@
   "author": "P.R. van der Wilt",
   "main": "settler.js",
   "scripts": {
-    "test": "node --test test/basic/*.test.js test/integration/*.test.js test/edge/*.test.js"
+    "test": "node --test test/basic/*.test.js test/integration/*.test.js test/edge/*.test.js",
+    "wiki:contract":  "node ../generalFunctions/scripts/wikiGen.js contract  ./src/commands/index.js   --write ./wiki/Home.md",
+    "wiki:datamodel": "node ../generalFunctions/scripts/wikiGen.js datamodel ./src/specificClass.js     --write ./wiki/Home.md",
+    "wiki:all":       "npm run wiki:contract && npm run wiki:datamodel"
   },
   "node-red": {
     "nodes": {

settler.html

@@ -3,7 +3,7 @@
 <script type="text/javascript">
   RED.nodes.registerType("settler", {
     category: "EVOLV",
-    color: "#e4a363",
+    color: "#8FAD3F",
     defaults: {
       name: { value: "" },
       processOutputFormat: { value: "process" },
@@ -70,6 +70,7 @@
     <label for="node-input-dbaseOutputFormat"><i class="fa fa-database"></i> Database Output</label>
     <select id="node-input-dbaseOutputFormat" style="width:60%;">
       <option value="influxdb">influxdb</option>
+      <option value="frost">frost</option>
       <option value="json">json</option>
       <option value="csv">csv</option>
     </select>

src/commands/handlers.js

@@ -5,11 +5,11 @@
 //   msg:    the Node-RED input message.
 //   ctx:    { node, RED, send, logger } — provided by BaseNodeAdapter.
 //
-// Settler currently accepts no behavioural commands — the legacy
-// `registerChild` topic is handled by the BaseNodeAdapter input dispatch
-// via the generalFunctions registry (`child.register` canonical) and the
-// node never had a public set/cmd surface beyond that. Future
-// influent-injection or operator-override topics will land here.
+// Settler accepts `child.register` (alias `registerChild`) on Port 0 input
+// to register measurement / reactor children, plus `data.influent` for
+// manual override. BaseNodeAdapter dispatches msg.topic through the
+// per-node registry — there is no implicit `child.register` handler in
+// the base, so it must be listed explicitly here.
 
 function _logger(source, ctx) {
   return ctx?.logger || source?.logger || null;
@@ -30,3 +30,16 @@ exports.dataInfluent = (source, msg, ctx) => {
   if (Array.isArray(p.C)) source.Cs_in = [...p.C];
   source.notifyOutputChanged();
 };
+
+// Inbound child registration from a measurement (or reactor) child.
+// Ported from the legacy `case 'registerChild'` branch in nodeClass.
+exports.childRegister = (source, msg, ctx) => {
+  const log = _logger(source, ctx);
+  const childId = msg.payload;
+  const childObj = ctx?.RED?.nodes?.getNode?.(childId);
+  if (!childObj?.source) {
+    log?.warn?.(`child.register skipped: missing child/source for id=${childId}`);
+    return;
+  }
+  source.childRegistrationUtils.registerChild(childObj.source, msg.positionVsParent, msg.distance);
+};

src/commands/index.js

@@ -12,6 +12,16 @@ module.exports = [
     topic: 'data.influent',
     aliases: ['influent', 'setInfluent'],
     payloadSchema: { type: 'any' },
+    // Compound payload `{F, C: [...]}` — registry-level units normalisation is
+    // skipped (the handler converts per-field internally; flow=m3/h, conc=mg/L).
+    description: 'Push the influent stream (payload: {F: flow m3/h, C: [concentrations mg/L]}).',
     handler: handlers.dataInfluent,
   },
+  {
+    topic: 'child.register',
+    aliases: ['registerChild'],
+    payloadSchema: { type: 'string' },
+    description: 'Register a child node (typically a measurement) with this settler.',
+    handler: handlers.childRegister,
+  },
 ];

wiki/Home.md

@@ -0,0 +1,134 @@
+# settler
+
+![code-ref](https://img.shields.io/badge/code--ref-a3583a3-blue) ![s88](https://img.shields.io/badge/S88-Unit-50a8d9) ![status](https://img.shields.io/badge/status-stub--level-lightgrey)
+
+A `settler` models a secondary clarifier — the sludge-separation stage that sits downstream of a biological reactor. It receives the upstream reactor's effluent stream, performs a 13-species TSS mass balance, and splits the result into three Fluent envelopes: clarified effluent, surplus sludge, and return sludge. A downstream return pump (a `rotatingMachine` registered as `machine` / `downstream`) draws the return-sludge flow.
+
+> [!NOTE]
+> Pending full node review (2026-05). Content reflects `CONTRACT.md` and current source only. The shipped `examples/` folder ships stubs only — production-grade flows are still TODO. Treat this page as informative, not authoritative.
+
+---
+
+## At a glance
+
+| Thing | Value |
+|:---|:---|
+| What it represents | Secondary clarifier / sludge settler — the gravity-separation stage between a biological reactor and its downstream sludge handling |
+| S88 level | Unit |
+| Use it when | You have a reactor whose effluent must be split into clarified water + return / surplus sludge by a TSS mass balance |
+| Don't use it for | Primary sedimentation (species 7–12 zeroing is wrong), generic mass-balance transforms (the 13-species ASM3 vector is hard-coded), single-tank SBRs that don't need a 3-stream split |
+| Children it accepts | `measurement` (any, but `quantity (tss)` is the only one that mutates state), `reactor` (upstream), `machine` (downstream — the return pump) |
+| Parents it talks to | Typically a downstream `reactor` — the three Fluent streams are routed by `payload.inlet` |
+
+---
+
+## How it fits
+
+```mermaid
+flowchart LR
+    upstream[reactor<br/>upstream<br/>Unit]:::unit
+    settler[settler<br/>Unit]:::unit
+    downstream[reactor<br/>downstream<br/>Unit]:::unit
+    return_pump[rotatingMachine<br/>return pump<br/>Equipment]:::equip
+    tss[measurement<br/>quantity tss<br/>atequipment]:::ctrl
+
+    upstream -.stateChange.-> settler
+    settler -->|Fluent inlet=0 effluent| downstream
+    settler -->|Fluent inlet=1 surplus| downstream
+    settler -->|Fluent inlet=2 return| return_pump
+    return_pump -->|child.register downstream| settler
+    tss -->|quantity tss.measured.atequipment| settler
+    classDef unit fill:#50a8d9,color:#000
+    classDef equip fill:#86bbdd,color:#000
+    classDef ctrl fill:#a9daee,color:#000
+```
+
+S88 colours are anchored in `.claude/rules/node-red-flow-layout.md`. The settler editor colour is currently `#e4a363` (orange) &mdash; tracked as drift in §16 of that rule; diagrams in this wiki use the correct Unit blue (`#50a8d9`).
+
+---
+
+## Try it &mdash; 1-minute demo
+
+> [!IMPORTANT]
+> The shipped examples (`examples/basic.flow.json`, `integration.flow.json`, `edge.flow.json`) are skeleton stubs &mdash; they create a settler node and a debug tap, but do not exercise the reactor &rarr; settler &rarr; pump chain. A proper Tier-1 / Tier-2 / Tier-3 example set is on the TODO list; until then this section walks the minimum stimulus.
+
+Import the basic stub, deploy, then drive influent manually:
+
+```bash
+curl -X POST -H 'Content-Type: application/json' \
+  --data @nodes/settler/examples/basic.flow.json \
+  http://localhost:1880/flow
+```
+
+After deploy, send one inject:
+
+| Topic | Payload | What it does |
+|:---|:---|:---|
+| `data.influent` | `{ "F": 1000, "C": [0,0,0,0,0,0,0,0,0,0,0,0,3000] }` | Pushes 1000 m³/h influent with 3000 mg/L total solids (index 12 = `X_TS`). Three Fluent envelopes appear on Port 0 immediately. |
+
+> [!NOTE]
+> Pending full node review (2026-05). Real flows (Tier-1 inject only, Tier-2 reactor + settler + pump, Tier-3 dashboard) are not yet shipped. See [Reference &mdash; Examples](Reference-Examples).
+
+---
+
+## The two things you'll send
+
+| Topic | Aliases | Payload | What it does |
+|:---|:---|:---|:---|
+| `data.influent` | `influent`, `setInfluent` | `{F: number, C: number[13]}` &mdash; either field optional | Override the influent stream directly. Triggers a recompute of all three Fluent envelopes. |
+| `child.register` | `registerChild` | `string` (child node id) | Register a `measurement`, `reactor`, or `machine` child. Port 2 wiring does this automatically in normal flows. |
+
+That is the entire input contract. Settler has no FSM, no setpoint, no startup sequence &mdash; it is a stateless transform on top of whatever the upstream reactor + measurement children push into it.
+
+---
+
+## What you'll see come out
+
+Sample Port 0 messages (one push, three envelopes):
+
+```json
+[
+  { "topic": "Fluent", "payload": { "inlet": 0, "F": 850.0, "C": [/*7-12 zeroed*/] }, "timestamp": 1715000000000 },
+  { "topic": "Fluent", "payload": { "inlet": 1, "F":  50.0, "C": [/*7-12 concentrated*/] }, "timestamp": 1715000000000 },
+  { "topic": "Fluent", "payload": { "inlet": 2, "F": 100.0, "C": [/*7-12 concentrated*/] }, "timestamp": 1715000000000 }
+]
+```
+
+| `payload.inlet` | Meaning | Particulate species (indices 7&ndash;12) |
+|:---:|:---|:---|
+| `0` | Clarified effluent | zeroed when `F_s > 0` |
+| `1` | Surplus sludge (the fraction the return pump does not draw) | concentrated by `F_in / F_s` |
+| `2` | Return sludge (drawn by the downstream return pump, capped at `F_s`) | concentrated by `F_in / F_s` |
+
+Mass balance invariant: `F_eff + F_surplus + F_return = F_in` (modulo float).
+
+Port 1 (InfluxDB) is the scalar dashboard view &mdash; see [Reference &mdash; Contracts](Reference-Contracts#data-model--getoutput-shape). Port 2 carries the one-shot `child.register` upward at startup.
+
+---
+
+## Capability matrix
+
+| Capability | Status | Notes |
+|:---|:---:|:---|
+| TSS mass-balance split (3 streams) | yes | `F_s = min(F_in * Cs[12] / C_TS, F_in)` &mdash; clamped to prevent negative effluent. |
+| Particulate zeroing in effluent | yes | Species 7&ndash;12 set to 0 in `inlet=0` when `F_s > 0`. |
+| Particulate concentration in sludge | yes | Species 7&ndash;12 scaled by `F_in / F_s` in `inlet=1` + `inlet=2`. |
+| Return-pump flow draw | yes | `F_sr = min(pump flow at equipment, F_s)`. Surplus = `F_s - F_sr`. |
+| `F_s` clamp to `F_in` | yes | Prevents negative effluent when `X_TS_in > C_TS`. |
+| Manual influent override | yes | `data.influent` lets ops supply `{F, C}` directly. |
+| Multiple reactor upstreams | no | Only one `upstreamReactor` slot; last registration wins. |
+| Stateful FSM | no | Stateless transform &mdash; recomputes on every trigger. |
+| Curve loading / drift / sequence-abort | n/a | Not applicable to a passive split. |
+
+---
+
+## Need more?
+
+| Page | What you'll find |
+|:---|:---|
+| [Reference &mdash; Contracts](Reference-Contracts) | Topic registry, config schema, child registration filters |
+| [Reference &mdash; Architecture](Reference-Architecture) | Three-tier code map, reactor &harr; settler wiring (the load-bearing bit), lifecycle, output ports |
+| [Reference &mdash; Examples](Reference-Examples) | Shipped example flows (currently stubs) + the TODO list for production-grade demos |
+| [Reference &mdash; Limitations](Reference-Limitations) | When not to use, known limitations, open questions |
+
+[EVOLV master wiki](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Home) &middot; [Topology Patterns](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topology-Patterns) &middot; [Topic Conventions](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topic-Conventions)

wiki/Reference-Architecture.md

@@ -0,0 +1,291 @@
+# Reference — Architecture
+
+![code-ref](https://img.shields.io/badge/code--ref-a3583a3-blue)
+
+> [!NOTE]
+> Pending full node review (2026-05). Content reflects `CONTRACT.md` and current source only.
+
+Code structure for `settler`: the three-tier sandwich, the `src/` layout, the reactor ↔ settler wiring (the load-bearing bit), the lifecycle, and the output-port pipeline. For an intuitive overview, return to [Home](Home).
+
+---
+
+## Three-tier code layout
+
+```
+nodes/settler/
+|
++-- settler.js                     entry: RED.nodes.registerType('settler', ...) + /settler/menu.js admin route
++-- settler.html                   editor form (Name, output formats, logger, position) — currently colour-drifted to #e4a363
+|
++-- src/
+|     nodeClass.js                 extends BaseNodeAdapter — domain wiring + Port 0/1 emit (~30 LOC)
+|     specificClass.js             extends BaseDomain — TSS split + child wiring (~140 LOC)
+|     |
+|     +-- commands/
+|           index.js               2 topic descriptors: data.influent (+aliases), child.register
+|           handlers.js            pure handler functions
+```
+
+Settler is small enough (~140 LOC of domain code) that no concern-split was needed; per the platform's MODULE_SPLIT contract a node only fans out into `src/<concern>/` modules when complexity demands it.
+
+### Tier responsibilities
+
+| Tier | File | What it owns | Touches `RED.*` |
+|:---|:---|:---|:---:|
+| entry | `settler.js` | Type registration + `/settler/menu.js` admin endpoint (proxies reactor's MenuManager). | yes |
+| nodeClass | `src/nodeClass.js` | `_emitOutputs()` only &mdash; calls `source.getEffluent` for the 3-msg Port-0 array and `source.getOutput()` for Port-1 InfluxDB telemetry. `tickInterval = null` (event-driven, no periodic loop). `statusInterval = 1000` for the badge. | yes |
+| specificClass | `src/specificClass.js` | `Settler.configure()` wires the `ChildRouter` for `measurement` / `reactor` / `machine` children. `getEffluent` is the mass-balance core. `getOutput` is the scalar Port-1 view. `getStatusBadge` renders the editor badge. | no |
+
+`specificClass` does the work directly; there is no orchestration / concern layer between it and the math.
+
+> [!NOTE]
+> Pending full node review (2026-05). The router-based registration uses `this.router.onRegister(...)` &mdash; verify against the latest BaseDomain contract when next touched.
+
+---
+
+## FSM
+
+Not applicable. Settler is **stateless**. There is no FSM, no `state.*` member, no `executeSequence`, no movement / setpoint. Every trigger (`stateChange` from the upstream reactor, `data.influent` from an operator, or a `quantity (tss)` update from a measurement child) causes a fresh recompute of the three Fluent envelopes from the current runtime state, and the split immediately re-emits.
+
+The status badge has two cosmetic branches only:
+
+| Condition | Badge |
+|:---|:---|
+| `F_in <= 0` | `statusBadge.idle('no influent')` |
+| else | green dot, label `F_in=<n> eff=<n> surplus=<n>` |
+
+There are no "protected states", no abort tokens, no allow-lists. All of that belongs to FSM-bearing nodes (`rotatingMachine`, `pumpingStation`, `machineGroupControl`, &hellip;).
+
+---
+
+## Reactor &harr; settler wiring &mdash; the load-bearing bit
+
+This is the one piece of settler that needs care, because the reactor uses a different event channel than every other child type in EVOLV.
+
+```mermaid
+flowchart TB
+    reactor[upstream reactor]:::unit
+    rEmit{reactor.emitter}
+    rMeas{reactor.measurements.emitter}
+    settler[settler._connectReactor]:::unit
+    pull[upstreamReactor.getEffluent]
+    apply[F_in = ...<br/>Cs_in = ...]
+    notify[notifyOutputChanged&#40;&#41;]
+
+    reactor --> rEmit
+    reactor --> rMeas
+    rEmit -- stateChange --> settler
+    rMeas -. NOT used .- settler
+    settler --> pull
+    pull --> apply
+    apply --> notify
+    classDef unit fill:#50a8d9,color:#000
+```
+
+Mechanism:
+
+1. The reactor pushes its `stateChange` event on `reactor.emitter` &mdash; **not** on `reactor.measurements.emitter`. The standard `router.onMeasurement` subscription path therefore can't see it.
+2. `_connectReactor(reactorChild)` attaches the listener manually:
+
+   ```js
+   reactorChild.emitter.on('stateChange', () => {
+     const raw = this.upstreamReactor.getEffluent;
+     const effluent = Array.isArray(raw) ? raw[0] : raw;
+     this.F_in = effluent.payload.F;
+     this.Cs_in = effluent.payload.C;
+     this.notifyOutputChanged();
+   });
+   ```
+
+3. `reactor.getEffluent` historically returned either an **array** (a 3-stream Fluent envelope, same shape settler itself emits) or a **single envelope** &mdash; the 2026-03-02 `_connectReactor` fix preserves both shapes via `Array.isArray(raw) ? raw[0] : raw`. If you change the reactor's effluent shape, this is the line to update.
+4. Position check: settler warns `Reactor children of settlers should be upstream.` if `positionVsParent !== 'upstream'`, but still stores the reactor. The wiring is not blocked &mdash; it just becomes the operator's problem to confirm intent.
+
+> [!NOTE]
+> Pending full node review (2026-05). The settler-side pull-not-push semantics rely on `reactor.getEffluent` being a property getter (no arguments). Future reactor refactors that turn this into a parameterised method will need a coordinated change here.
+
+---
+
+## Return-pump wiring
+
+`_connectMachine(machineChild)` is the second non-trivial registration path:
+
+| Condition | Effect |
+|:---|:---|
+| `positionVsParent === 'downstream'` | Store as `this.returnPump`. Set `machineChild.upstreamSource = this` so the pump's own flow predictor can use settler's `inlet=2` envelope as its suction-side Fluent. |
+| else | Warn `Failed to register machine child.`, no storage. |
+
+At each call to `getEffluent`, settler reads the pump's current measured flow:
+
+```js
+F_sr = Math.min(
+  this.returnPump.measurements.type('flow').variant('measured').position(POSITIONS.AT_EQUIPMENT).getCurrentValue(),
+  F_s,
+);
+```
+
+If no return pump is registered or its flow measurement is zero, `F_sr = 0` &mdash; in that case all separated sludge becomes surplus (`inlet=1`) and the return stream (`inlet=2`) is zero-flow.
+
+---
+
+## Measurement-child wiring
+
+`_connectMeasurement(measurementChild)` is generic: it subscribes to `<type>.measured.<position>` on the child's `measurements.emitter` and:
+
+1. Re-emits the value on settler's own `this.measurements` container (lets settler's own parent subscribe).
+2. Calls `_updateMeasurement(type, value, position, eventData)`.
+
+`_updateMeasurement` currently recognises only one type:
+
+| `measurementType` | Side-effect |
+|:---|:---|
+| `quantity (tss)` | Set `this.C_TS = value`. Trigger `notifyOutputChanged()`. |
+| anything else | Log an `error` (`Type '<type>' not recognized for measured update.`) &mdash; the re-emit still happened, just no settler-side state change. |
+
+The `quantity (tss)` value is the **settler's own setpoint** for the target return-sludge concentration. The default is `2500` mg/L. Higher `C_TS` &rarr; less return + surplus, more effluent. Lower `C_TS` &rarr; more return + surplus.
+
+---
+
+## Mass-balance math (`getEffluent`)
+
+```mermaid
+flowchart TB
+    F_in[F_in m³/h]:::input
+    Cs_in[Cs_in array 13<br/>mg/L per species]:::input
+    C_TS[C_TS<br/>target return mg/L]:::input
+    pumpFlow[returnPump.flow.measured.atequipment]:::input
+
+    F_in --> Fs[F_s = min&#40;F_in × Cs_in&#91;12&#93; / C_TS, F_in&#41;]
+    Cs_in --> Fs
+    C_TS --> Fs
+    Fs --> F_eff[F_eff = F_in − F_s]
+    Fs --> F_sr[F_sr = min&#40;pumpFlow, F_s&#41;]
+    pumpFlow --> F_sr
+    F_sr --> F_so[F_so = F_s − F_sr]
+
+    Cs_in --> CsEff[Cs_eff: copy then zero 7..12 if F_s > 0]
+    Cs_in --> CsS[Cs_s: copy then scale 7..12 by F_in / F_s if F_s > 0]
+
+    F_eff --> envEff[envelope inlet=0]
+    CsEff --> envEff
+    F_so --> envSur[envelope inlet=1]
+    CsS --> envSur
+    F_sr --> envRet[envelope inlet=2]
+    CsS --> envRet
+    classDef input fill:#a9daee,color:#000
+```
+
+Key facts:
+
+- `F_s` is the **total separated sludge stream**. Mass-balance derivation: at steady state, `F_in * Cs_in[12] = F_s * C_TS` &rarr; `F_s = F_in * Cs_in[12] / C_TS`.
+- The clamp `min(..., F_in)` prevents `F_eff` going negative when `Cs_in[12] > C_TS` (i.e. the influent is denser than the target sludge concentration). Sub-rosa: the clamp masks the **upstream** problem; settler does not warn when the clamp fires &mdash; see [Reference &mdash; Limitations](Reference-Limitations#no-flow-balance-warning).
+- Species indices 7&ndash;12 are the ASM3 particulate species (`X_*`). Index 12 specifically is `X_TS` &mdash; the lumped total-suspended-solids surrogate the split is keyed off.
+- Soluble species 0&ndash;6 pass through unchanged in all three streams.
+- All three envelopes share a single `timestamp = Date.now()` &mdash; downstream consumers can rely on them being a coherent triple.
+
+---
+
+## Lifecycle &mdash; what one trigger does
+
+```mermaid
+sequenceDiagram
+    autonumber
+    participant reactor as upstream reactor
+    participant settler as settler (specificClass)
+    participant nc as nodeClass
+    participant pump as return pump child
+    participant out as Port 0 / 1
+
+    reactor->>settler: emitter.emit('stateChange')
+    settler->>reactor: read getEffluent
+    reactor-->>settler: {F, C[13]} (or [{...}])
+    settler->>settler: F_in = F · Cs_in = C
+    settler->>settler: notifyOutputChanged()
+    nc->>settler: read getEffluent (recompute)
+    settler->>pump: read measurements.flow.measured.atequipment
+    pump-->>settler: returnFlow (m³/h)
+    settler->>settler: getEffluent — split into 3 envelopes
+    settler-->>nc: [Fluent inlet=0, inlet=1, inlet=2]
+    nc->>settler: read getOutput()
+    settler-->>nc: {F_in, C_TS, F_eff, F_surplus, F_return, ...measurements}
+    nc->>out: send([fluent, influxMsg, null])
+```
+
+The three triggers that route through this lifecycle are:
+
+| Trigger | Origin | Path |
+|:---|:---|:---|
+| Reactor `stateChange` | `reactor.emitter.emit('stateChange')` | `_connectReactor` listener &rarr; pull `getEffluent` &rarr; copy &rarr; `notifyOutputChanged` |
+| Operator `data.influent` | Inbound `msg.topic` | `commands/handlers.js#dataInfluent` &rarr; mutate `F_in` / `Cs_in` &rarr; `notifyOutputChanged` |
+| Measurement `quantity (tss)` | `measurementChild.measurements.emitter` | `_connectMeasurement` re-emit + `_updateMeasurement` &rarr; mutate `C_TS` &rarr; `notifyOutputChanged` |
+
+`notifyOutputChanged` is BaseDomain's standard `output-changed` event. `BaseNodeAdapter` listens, calls `_emitOutputs()`, which produces the Port 0 / Port 1 messages.
+
+---
+
+## Output ports
+
+| Port | Carries | Sample shape |
+|:---|:---|:---|
+| 0 (process) | **Array of three Node-RED messages**, each `{topic: 'Fluent', payload: {inlet, F, C}, timestamp}`. Re-emitted on every recompute. | See [Home &mdash; What you'll see come out](Home#what-youll-see-come-out). |
+| 1 (telemetry) | Single InfluxDB line-protocol payload built by `outputUtils.formatMsg(getOutput(), cfg, 'influxdb')`. Delta-compressed: only changed fields shipped. | `settler,id=settler_a F_in=1000,F_eff=850,F_surplus=50,F_return=100,C_TS=2500,...` |
+| 2 (register / control) | `null` from `_emitOutputs`. The one-shot `child.register` upward at startup goes through the BaseNodeAdapter init path, not `_emitOutputs`. | `{topic: 'child.register', payload: <node.id>, positionVsParent, distance}` (init only) |
+
+Port-1 key shape from `getOutput()`:
+
+| Key | Type | Source | Notes |
+|:---|:---|:---|:---|
+| `F_in` | number | `host.F_in` | Influent flow (m³/h). |
+| `C_TS` | number | `host.C_TS` | Target return-sludge concentration (mg/L). Default 2500. |
+| `F_eff` | number | `streams[0].payload.F` | Clarified effluent flow. |
+| `F_surplus` | number | `streams[1].payload.F` | Surplus sludge flow. |
+| `F_return` | number | `streams[2].payload.F` | Return sludge flow. |
+| `<type>.<variant>.<position>.<childId>` | varies | `measurements.getFlattenedOutput()` | Flattened snapshot of every measurement settler has seen (re-emitted from children). |
+
+See [EVOLV &mdash; Telemetry](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Telemetry) for the full InfluxDB layout.
+
+> [!NOTE]
+> Pending full node review (2026-05). The `getOutput()` return shape has not been audited against an `_output-manifest.md` (the output-coverage rule). TODO: add the manifest and `test/basic/output-*.test.js` coverage in both populated and degraded states (no influent / no pump / no TSS measurement).
+
+---
+
+## Event sources
+
+| Source | Where it fires | What it triggers |
+|:---|:---|:---|
+| `reactor.emitter` `'stateChange'` | Upstream reactor on every internal state advance | `_connectReactor` listener &rarr; pull `getEffluent` &rarr; recompute |
+| `measurementChild.measurements.emitter` `'<type>.measured.<position>'` | Any registered measurement child on a new sample | `_connectMeasurement` re-emit + `_updateMeasurement` switch |
+| Inbound `msg.topic = data.influent` | Node-RED input wire | `commands/handlers.js#dataInfluent` |
+| Inbound `msg.topic = child.register` | Node-RED input wire (rare; usually Port 2 wiring) | `commands/handlers.js#childRegister` |
+| `BaseDomain` `'output-changed'` | `notifyOutputChanged()` in domain | `nodeClass._emitOutputs()` |
+| `setInterval(statusInterval = 1000)` | `BaseNodeAdapter` | Re-render the status badge |
+
+No per-second tick on the domain itself. `tickInterval = null` is explicit in `nodeClass`.
+
+---
+
+## Where to start reading
+
+| If you're changing&hellip; | Read first |
+|:---|:---|
+| The TSS mass-balance math | `src/specificClass.js#getEffluent` (lines 37&ndash;62) |
+| Reactor &harr; settler wiring (stateChange listener, both-shape envelope handling) | `src/specificClass.js#_connectReactor` |
+| Return-pump wiring (the `machine` / `downstream` registration) | `src/specificClass.js#_connectMachine` |
+| Measurement re-emit + `C_TS` setpoint | `src/specificClass.js#_connectMeasurement` + `#_updateMeasurement` |
+| Operator-side influent override | `src/commands/handlers.js#dataInfluent` |
+| Port 0 (3-msg array) + Port 1 (InfluxDB) emit pipeline | `src/nodeClass.js#_emitOutputs` |
+| Status-badge text | `src/specificClass.js#getStatusBadge` |
+| Editor form / colour drift | `settler.html` (currently `color: '#e4a363'`; should be `#50a8d9`) |
+
+---
+
+## Related pages
+
+| Page | Why |
+|:---|:---|
+| [Home](Home) | Intuitive overview |
+| [Reference &mdash; Contracts](Reference-Contracts) | Topic + config + child filters |
+| [Reference &mdash; Examples](Reference-Examples) | Shipped flows + debug recipes |
+| [Reference &mdash; Limitations](Reference-Limitations) | Known issues and open questions |
+| [reactor wiki](https://gitea.wbd-rd.nl/RnD/reactor/wiki/Home) | The upstream parent &mdash; emits `stateChange` and exposes `getEffluent` |
+| [rotatingMachine wiki](https://gitea.wbd-rd.nl/RnD/rotatingMachine/wiki/Home) | The return-pump child &mdash; consumes `inlet=2` via `upstreamSource` |
+| [EVOLV &mdash; Architecture](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Architecture) | Platform-wide three-tier pattern |

wiki/Reference-Contracts.md

@@ -0,0 +1,176 @@
+# Reference — Contracts
+
+![code-ref](https://img.shields.io/badge/code--ref-a3583a3-blue)
+
+> [!NOTE]
+> Pending full node review (2026-05). Content reflects `CONTRACT.md`, `src/commands/index.js`, and `generalFunctions/src/configs/settler.json` only.
+
+Full topic contract, configuration schema, and child-registration filters for `settler`. Source of truth: `src/commands/index.js`, `src/specificClass.js` `configure()`, and the schema at `generalFunctions/src/configs/settler.json`. For an intuitive overview, return to the [Home](Home).
+
+---
+
+## Topic contract
+
+The registry lives in `src/commands/index.js`. Each descriptor maps a canonical `msg.topic` to its handler; aliases emit a one-time deprecation warning the first time they fire.
+
+<!-- BEGIN AUTOGEN: topic-contract -->
+
+| Canonical topic | Aliases | Payload | Unit | Effect |
+|---|---|---|---|---|
+| `data.influent` | `influent`, `setInfluent` | any | — | Push the influent stream (payload: {F: flow m3/h, C: [concentrations mg/L]}). |
+| `child.register` | `registerChild` | `string` | — | Register a child node (typically a measurement) with this settler. |
+
+<!-- END AUTOGEN: topic-contract -->
+
+> [!NOTE]
+> Pending full node review (2026-05). The autogen markers above will be populated by a future `npm run wiki:contract` tool. Until then the table is hand-maintained against `src/commands/index.js`.
+
+### Mode / source / action allow-lists
+
+**Not applicable.** Settler has no operational mode, no source allow-list, no action allow-list. Both topics are accepted unconditionally; payload-shape validation lives in the handler itself.
+
+The `data.influent` handler validates:
+
+```js
+if (!p || typeof p !== 'object' || Array.isArray(p)) {
+  log?.warn?.(`data.influent expects an object {F, C}; got ${typeof p}`);
+  return;
+}
+if (typeof p.F === 'number' && Number.isFinite(p.F)) source.F_in = p.F;
+if (Array.isArray(p.C)) source.Cs_in = [...p.C];
+```
+
+Non-finite or non-numeric `F` is silently ignored. Non-array `C` is silently ignored. Either field may be omitted to update only the other. Negative `F` is **not** rejected &mdash; the downstream `getEffluent` math will produce nonsense but the node will not throw.
+
+---
+
+## Data model &mdash; `getOutput()` shape
+
+Composed each tick by `src/specificClass.js` `getOutput()`. Port 0 carries the 3-message Fluent stream **directly** (not via `getOutput`); Port 1 (this snapshot) is the scalar dashboard view.
+
+<!-- BEGIN AUTOGEN: data-model — populate via wiki-gen tool (TODO) -->
+
+### Scalar keys
+
+| Key | Type | Unit | Source | Notes |
+|:---|:---|:---|:---|:---|
+| `F_in` | number | m³/h | `host.F_in` | Influent flow. Default 0. |
+| `C_TS` | number | mg/L | `host.C_TS` | Target return-sludge concentration. Default 2500. Updated by `quantity (tss)` measurement child. |
+| `F_eff` | number | m³/h | `streams[0].payload.F` | Clarified effluent flow. |
+| `F_surplus` | number | m³/h | `streams[1].payload.F` | Surplus sludge flow (`F_s - F_sr`). |
+| `F_return` | number | m³/h | `streams[2].payload.F` | Return sludge flow (`min(pumpFlow, F_s)`). |
+
+### Per-measurement keys
+
+For every `(type, variant, position)` stored in `this.measurements` MeasurementContainer, the flattened output emits:
+
+```
+<type>.<variant>.<position>.<childId>
+```
+
+Position labels are normalised to lowercase. The trailing `<childId>` is the registering measurement child's id. Settler does not write its own measurements directly &mdash; every key in this group came from a registered child (the `_connectMeasurement` re-emit).
+
+<!-- END AUTOGEN: data-model -->
+
+### Status badge
+
+`getStatusBadge()` in `src/specificClass.js`:
+
+| Condition | Badge |
+|:---|:---|
+| `F_in <= 0` | `statusBadge.idle('no influent')` (grey ring) |
+| else | green dot, label `F_in=<n.nn> eff=<n.nn> surplus=<n.nn>` (m³/h, 2 dp) |
+
+No state-symbol enumeration &mdash; settler has no FSM.
+
+---
+
+## Configuration schema &mdash; editor form to config keys
+
+Source of truth: `generalFunctions/src/configs/settler.json` plus `settler.html`.
+
+### General (`config.general`)
+
+| Form field | Config key | Default | Notes |
+|:---|:---|:---|:---|
+| Name | `general.name` | `"Settler"` | Human-readable name. |
+| (auto-assigned) | `general.id` | `null` | Node-RED node id. |
+| Default unit | `general.unit` | `null` | Default measurement unit. Currently unused by settler &mdash; child measurements carry their own units. |
+| Enable logging | `general.logging.enabled` | `true` | Master switch. |
+| Log level | `general.logging.logLevel` | `info` | `debug` / `info` / `warn` / `error`. |
+
+### Functionality (`config.functionality`)
+
+| Form field | Config key | Default | Notes |
+|:---|:---|:---|:---|
+| (hidden) | `functionality.softwareType` | `settler` | Constant. Used by the parent's router as a registration filter. |
+| (hidden) | `functionality.role` | `Secondary settler for sludge separation` | Documentation string. |
+| Position vs parent | `functionality.positionVsParent` | `downstream` | One of `upstream` / `atEquipment` / `downstream`. Settler typically registers as `downstream` against an upstream reactor. |
+
+### Node-RED-side (editor form, not domain config)
+
+| Form field | Stored on | Default | Notes |
+|:---|:---|:---|:---|
+| Process Output Format | `nodeClass.processOutputFormat` | `process` | `process` / `json` / `csv`. Port-0 serialisation. |
+| Database Output Format | `nodeClass.dbaseOutputFormat` | `influxdb` | `influxdb` / `json` / `csv`. Port-1 serialisation. |
+
+`buildDomainConfig()` returns `{}` &mdash; settler does not push any editor-derived values into the domain at start-up. All operational state is runtime (`F_in`, `Cs_in`, `C_TS`).
+
+> [!NOTE]
+> Pending full node review (2026-05). The editor form (`settler.html`) is currently colour-drifted to `#e4a363` (orange); should be `#50a8d9` (Unit blue) per `.claude/rules/node-red-flow-layout.md` §16.
+
+### Unit policy
+
+| Quantity | Canonical (internal) | Output (Port 1) | Notes |
+|:---|:---|:---|:---|
+| Flow (`F_in`, `F_eff`, `F_surplus`, `F_return`) | m³/h | m³/h | No conversion &mdash; settler is unit-agnostic above the storage layer. |
+| Concentration (`C_TS`, `Cs_in[*]`) | mg/L | mg/L | Same. |
+
+> [!NOTE]
+> Pending full node review (2026-05). Settler does **not** declare a `requireUnitForTypes` policy via MeasurementContainer; verify against the general unit policy before relying on internal canonicalisation.
+
+---
+
+## Child registration
+
+Source: `src/specificClass.js` `configure()` (the `this.router.onRegister(...)` chain) and the three `_connect*` methods.
+
+| Software type | Filter | Wired to | Side-effect |
+|:---|:---|:---|:---|
+| `measurement` | any (no asset-type / position filter at register time) | `_connectMeasurement(child)` | Subscribes to `<type>.measured.<position>` on the child's `measurements.emitter`. Re-emits on settler's own MeasurementContainer (lets settler's parent see the value). `quantity (tss)` updates `C_TS`; anything else logs an `error` from `_updateMeasurement` but the re-emit still happened. |
+| `reactor` | `positionVsParent === 'upstream'` (warns otherwise but still registers) | `_connectReactor(child)` | Stored as `this.upstreamReactor`. Listener attached **manually** to `reactor.emitter` (NOT `measurements.emitter`) for `'stateChange'`; on fire, settler pulls `reactor.getEffluent` and copies `F_in` + `Cs_in`. Handles both array and single-envelope `getEffluent` shapes. |
+| `machine` | `positionVsParent === 'downstream'` (warns + skips otherwise) | `_connectMachine(child)` | Stored as `this.returnPump`. Settler reads `returnPump.measurements.type('flow').variant('measured').position('atEquipment').getCurrentValue()` to determine `F_sr`. Sets `machineChild.upstreamSource = this` so the pump can use settler's `inlet=2` Fluent as its suction-side context. |
+
+> [!NOTE]
+> Pending full node review (2026-05). The `measurement` filter accepts any asset-type at register time; only the runtime `_updateMeasurement` switch acts on `quantity (tss)`. Other measurement types are silently re-emitted but not consumed. TODO: decide whether this is desired (pass-through telemetry) or a contract gap.
+
+### No virtual children
+
+Unlike `rotatingMachine`, settler does **not** auto-register any virtual measurement children. Every measurement must come from an explicitly wired child node.
+
+---
+
+## Parent relationship
+
+Settler typically registers as `softwareType: 'settler'` with `positionVsParent: 'downstream'` against a reactor (the reactor's downstream stage). The downstream reactor consumes the three Fluent streams via `payload.inlet`:
+
+| `inlet` | Consumer expectation |
+|:---|:---|
+| `0` (clarified effluent) | Routed onward to the next process unit. |
+| `1` (surplus sludge) | Typically routed to a sludge-handling process (digestion, thickening, dewatering). |
+| `2` (return sludge) | Drawn back to a reactor inlet or the head of the biological train. |
+
+Multi-reactor settlers are **not supported** &mdash; `this.upstreamReactor` is a single slot; the last `child.register` call wins.
+
+---
+
+## Related pages
+
+| Page | Why |
+|:---|:---|
+| [Home](Home) | Intuitive overview |
+| [Reference &mdash; Architecture](Reference-Architecture) | Code map, reactor &harr; settler wiring, mass-balance math |
+| [Reference &mdash; Examples](Reference-Examples) | Shipped flows + debug recipes |
+| [Reference &mdash; Limitations](Reference-Limitations) | Known issues and open questions |
+| [EVOLV &mdash; Topic Conventions](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topic-Conventions) | Platform-wide topic rules |
+| [EVOLV &mdash; Telemetry](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Telemetry) | Port 0 / 1 / 2 InfluxDB layout |

wiki/Reference-Examples.md

@@ -0,0 +1,139 @@
+# Reference — Examples
+
+![code-ref](https://img.shields.io/badge/code--ref-a3583a3-blue)
+
+> [!NOTE]
+> Pending full node review (2026-05). The shipped example flows are **stub level**: each is a 4-node skeleton (tab + node + inject + debug) that proves the node loads in Node-RED but does **not** exercise the reactor → settler → return-pump chain or the TSS mass-balance math. Production-grade examples are TODO. See [Reference — Limitations — Example flows](Reference-Limitations#example-flows-are-stub-level).
+
+---
+
+## Shipped examples
+
+| File | Tier | Dependencies | What it shows |
+|:---|:---:|:---|:---|
+| `basic.flow.json` | 1 (stub) | EVOLV only | Loads a single settler node, wires a `ping` inject to its input, taps Port 0 (only) to a debug node. Inject payload is the string `"1"` — will be rejected by `data.influent`'s payload validator (warn logged). Useful only to verify the node type registers. |
+| `integration.flow.json` | 2 (stub) | EVOLV only | Same shape; inject sends `topic = registerChild`, payload `example-child-id`. The lookup will fail (no such node) and log a warn. Does **not** exercise reactor or pump wiring. |
+| `edge.flow.json` | 3 (stub) | EVOLV only | Same shape; inject sends `topic = doesNotExist`. Verifies the registry rejects unknown topics. |
+
+### Status
+
+| Aspect | State |
+|:---|:---|
+| Loads in Node-RED on deploy | yes |
+| Drives `data.influent` with a valid payload | no |
+| Drives the reactor → settler → return-pump chain | no |
+| Shows the 3-stream Fluent split on Port 0 | no |
+| Has a dashboard tier | no |
+| Validated against a live Node-RED instance | no |
+
+---
+
+## Loading a flow
+
+### Via the editor
+
+1. Open the Node-RED editor at `http://localhost:1880`.
+2. Menu → Import → drag the JSON file.
+3. Click Deploy.
+
+### Via the Admin API
+
+```bash
+curl -X POST -H 'Content-Type: application/json' \
+  --data @nodes/settler/examples/basic.flow.json \
+  http://localhost:1880/flows
+```
+
+---
+
+## TODO — production-grade example set
+
+The matching `rotatingMachine` repo ships three tiers; settler needs the same. Tracking placeholder:
+
+| Tier | Proposed filename | What it should show |
+|:---|:---|:---|
+| 1 | `01 - Basic Manual Influent.json` | Single settler + inject sending `data.influent` with a realistic `{F, C}` payload. Three debug taps (one per Port 0 stream by `payload.inlet`). Operator can vary F and watch the split rebalance. |
+| 2 | `02 - Reactor and Return Pump.json` | One `reactor` (upstream) + one `settler` + one `rotatingMachine` (return pump, downstream). Auto-registration via Port 2. Drive the reactor with an inject; settler should re-split on every reactor `stateChange`. |
+| 3 | `03 - Dashboard Visualization.json` | FlowFuse Dashboard 2.0 page: F_in / F_eff / F_surplus / F_return trend chart, C_TS gauge, status badges per stream. Required: `@flowfuse/node-red-dashboard` installed. |
+
+> [!IMPORTANT]
+> **Screenshots needed** once the production-grade examples land. Save as `wiki/_partial-screenshots/settler/01-basic-editor.png`, `02-reactor-pump-editor.png`, `03-dashboard-rendered.png`, ≤ 200 KB each.
+
+---
+
+## What the basic example would do (sketch — not yet shipped)
+
+Operator workflow once a real Tier-1 ships:
+
+1. Deploy the flow.
+2. Send `data.influent` with payload:
+
+   ```json
+   { "F": 1000, "C": [0,0,0,0,0,0,0,30,80,400,200,80,3000] }
+   ```
+
+   Twelve soluble species at low concentrations + index 12 `X_TS = 3000` mg/L.
+3. Observe three Port-0 messages arrive simultaneously, each with `topic = "Fluent"` and `payload.inlet` ∈ {0, 1, 2}.
+4. With default `C_TS = 2500` mg/L:
+   - `F_s = 1000 * 3000 / 2500 = 1200` — but clamped to `F_in = 1000`. **The clamp fires** — this is the input edge case [Reference — Limitations — no-flow-balance warning](Reference-Limitations#no-flow-balance-warning) refers to.
+   - `F_eff = 0`. The clarified-effluent envelope carries zero flow but still has its `C` vector (with species 7–12 zeroed).
+   - `F_sr` is 0 (no pump wired) → `F_surplus = 1000`, `F_return = 0`.
+5. Send `data.influent` with `X_TS = 1500` mg/L instead. Now `F_s = 600`, `F_eff = 400`, `F_surplus = 600`, `F_return = 0`. Realistic split.
+
+> [!NOTE]
+> Pending full node review (2026-05). The clamp-fires behaviour above is intended (per code comment in `getEffluent`) but produces no operator-visible warning. Tracked.
+
+---
+
+## Docker compose snippet
+
+To bring up Node-RED + InfluxDB with EVOLV nodes pre-loaded:
+
+```yaml
+# docker-compose.yml (extract)
+services:
+  nodered:
+    build: ./docker/nodered
+    ports: ['1880:1880']
+    volumes:
+      - ./docker/nodered/data:/data/evolv
+  influxdb:
+    image: influxdb:2.7
+    ports: ['8086:8086']
+```
+
+Full file: [EVOLV/docker-compose.yml](https://gitea.wbd-rd.nl/RnD/EVOLV/src/branch/development/docker-compose.yml).
+
+---
+
+## Debug recipes
+
+> [!NOTE]
+> Pending full node review (2026-05). Recipes below are grounded in the source; the symptom-side has not been confirmed against a live deployment.
+
+| Symptom | First thing to check | Where to look |
+|:---|:---|:---|
+| `F_eff` negative or `NaN` | `C_TS` is zero or `Cs_in[12]` is huge. The `F_s` clamp should prevent negatives — confirm the clamp `min(..., F_in)` is present. Likely the clamp fires but masks a deeper input problem. | `src/specificClass.js#getEffluent` line `const F_s = Math.min(...)`. |
+| Settler never updates after reactor changes | Reactor child is not on `'upstream'` position (warn logged but registration proceeds), or the listener is attached to the wrong emitter. | `_connectReactor` — listens on `reactor.emitter`, **NOT** `reactor.measurements.emitter`. |
+| Return-sludge flow stays at 0 | `returnPump.measurements.type('flow').variant('measured').position('atEquipment')` has no current value. Wire a flow measurement child on the pump (with `asset.type='flow'`, `positionVsParent='atEquipment'`). | `_connectMachine`, pump's MeasurementContainer chain. |
+| Three Fluent envelopes do not arrive at the downstream consumer | `payload.inlet` selector on the downstream reactor / pump mismatches (0 = effluent, 1 = surplus, 2 = return). | The downstream consumer's inlet routing. |
+| `quantity (tss)` updates don't change `C_TS` | Measurement child's `asset.type` must be the literal string `"quantity (tss)"` (with the space + parenthesised "tss"). | `src/specificClass.js#_updateMeasurement` switch case. |
+| `data.influent` inject is silently dropped | Payload must be an object `{F, C}`. A string, number, or array logs a warn (`data.influent expects an object {F, C}; got <type>`) and short-circuits. | `src/commands/handlers.js#dataInfluent`. |
+| Settler logs an `error` `Type '<x>' not recognized for measured update.` | A measurement child has registered with an `asset.type` settler doesn't recognise. The re-emit still happened &mdash; the error is about the absence of a `_updateMeasurement` switch case. Currently only `quantity (tss)` mutates state. | `_updateMeasurement`. |
+| `child.register` topic logs `child.register skipped: missing child/source for id=<x>` | The given node id doesn't resolve to a Node-RED node with a `.source` (i.e. an EVOLV domain). Verify the id is correct and the target node has already been deployed. | `src/commands/handlers.js#childRegister`. |
+| Status badge stuck on `idle: no influent` | `F_in <= 0`. Either no reactor has fired `stateChange` yet, or `data.influent` has not been sent with a positive `F`. | `src/specificClass.js#getStatusBadge`. |
+
+> Never ship `enableLog: 'debug'` in a demo &mdash; fills the container log within seconds and obscures real errors.
+
+---
+
+## Related pages
+
+| Page | Why |
+|:---|:---|
+| [Home](Home) | Intuitive overview |
+| [Reference &mdash; Contracts](Reference-Contracts) | Topic + config + child filters |
+| [Reference &mdash; Architecture](Reference-Architecture) | Code map, reactor &harr; settler wiring, mass-balance math |
+| [Reference &mdash; Limitations](Reference-Limitations) | Known issues and open questions |
+| [reactor &mdash; Examples](https://gitea.wbd-rd.nl/RnD/reactor/wiki/Reference-Examples) | The upstream parent &mdash; how to drive `stateChange` |
+| [EVOLV &mdash; Topology Patterns](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topology-Patterns) | Where settler fits in a larger plant |

wiki/Reference-Limitations.md

@@ -0,0 +1,116 @@
+# Reference — Limitations
+
+![code-ref](https://img.shields.io/badge/code--ref-a3583a3-blue)
+
+> [!NOTE]
+> Pending full node review (2026-05). What `settler` does not do, current rough edges, and open questions. Open items live in `.agents/improvements/IMPROVEMENTS_BACKLOG.md` in the superproject.
+
+---
+
+## When you would not use this node
+
+| Scenario | Use instead |
+|:---|:---|
+| Primary sedimentation upstream of biological treatment | The species 7–12 zeroing in the effluent stream is wrong for primary sludge (the soluble / particulate split is different). Model as a separate node. |
+| Generic mass-balance transform | The 13-species ASM3 concentration vector is hard-coded; `Cs[12]` (`X_TS`) is the only species the split is keyed off. Not a fit for arbitrary stream-splitting. |
+| Single-tank SBR with no separation stage | The 3-stream output expects a downstream consumer that routes by `payload.inlet`. A direct reactor → reactor wire is lighter. |
+| A reactor — you want to model biological transformation, not separation | `reactor` (settler is a passive separator, not a biological process). |
+| A return-pump itself — you want to model the pump's behaviour | `rotatingMachine` (settler reads the pump's measured flow but does not control it). |
+
+---
+
+## Known limitations
+
+### Example flows are stub level
+
+The three shipped flows (`basic.flow.json`, `integration.flow.json`, `edge.flow.json`) are 4-node skeletons (tab + node + inject + debug). They prove the node loads in Node-RED but do not exercise the reactor → settler → pump chain, do not drive `data.influent` with a valid payload, and do not have a dashboard tier. Production-grade examples are TODO — see [Reference — Examples — TODO](Reference-Examples#todo--production-grade-example-set).
+
+### Editor colour drift
+
+`settler.html` declares `color: '#e4a363'` (orange). The S88 Unit level requires `#50a8d9` (blue). The placement-rule registry (`.claude/rules/node-red-flow-layout.md` §14) already maps `settler` to the `UN` lane regardless of editor colour, so demos lay out correctly; the cosmetic mismatch is tracked in §16 of the same rule and is on the colour-cleanup list. The wiki diagrams use the correct blue.
+
+### Single-reactor upstream slot
+
+`this.upstreamReactor` is a single slot. Registering a second `reactor` child with `positionVsParent='upstream'` silently overwrites the first — the listener on the previous reactor's `emitter` is not detached, so it keeps firing into a settler that will pull effluent from the new reactor instead. Tracked.
+
+### `X_TS` index is hard-coded
+
+The mass balance uses `Cs_in[12]` (the ASM3 `X_TS` lumped solids species) as the surrogate for total suspended solids. Any change to the species ordering in the upstream reactor breaks settler. The coupling is not documented in the schema — it lives only in the `getEffluent` math and the `_updateMeasurement` switch case for `quantity (tss)`. Tracked.
+
+### No flow-balance warning
+
+When influent solids exceed the target return concentration (`Cs_in[12] > C_TS`), `F_s` is clamped to `F_in` and clarified effluent drops to zero. This is mathematically correct but masks an upstream problem (overloaded reactor, miscalibrated `C_TS` setpoint). The clamp fires silently &mdash; no warn, no badge change beyond the eventual `F_in <= 0` idle state. Operator must monitor `F_eff` directly. Tracked.
+
+### `quantity (tss)` measurement passes through but doesn't validate
+
+`_connectMeasurement` re-emits every measurement type, but `_updateMeasurement` only acts on `quantity (tss)`. Other types log an `error` (`Type '<x>' not recognized for measured update.`) but the re-emit already happened &mdash; the parent of settler still sees the value. Whether this is desired (settler acts as telemetry pass-through) or a contract gap is unresolved.
+
+> [!NOTE]
+> Pending full node review (2026-05). Open question: should `_connectMeasurement` filter by asset-type at register time and reject non-`quantity (tss)` children, or continue accepting everything as pass-through telemetry?
+
+### No output manifest / no degraded-state coverage
+
+Per the platform output-coverage rule (`.claude/rules/output-coverage.md`), every node needs a `test/_output-manifest.md` enumerating every Port 0 / 1 / 2 key and a `test/basic/output-*.test.js` exercising each one in both populated **and** degraded states. Settler has neither. The most likely degraded-state crash points:
+
+- Port 0 emitted before any reactor `stateChange` &mdash; `F_in = 0`, `Cs_in = [0...]`, the three envelopes carry zero flow but valid (zero) `C` arrays. Should not crash a downstream consumer, but un-tested.
+- Port 0 with `returnPump` registered but no flow measurement landed yet &mdash; `returnPump.measurements.type('flow').variant('measured').position('atEquipment').getCurrentValue()` returns `undefined` &rarr; `Math.min(undefined, F_s) = NaN`. `F_sr` becomes `NaN` &rarr; both `inlet=1` and `inlet=2` carry `NaN` flow.
+
+Tracked. TODO before trial-readiness: add the manifest, tests, and `null`-flow-measurement handling.
+
+### `reactor.getEffluent` shape coupling
+
+`_connectReactor` does `Array.isArray(raw) ? raw[0] : raw` to absorb both the older single-envelope shape and the newer 3-stream array shape of `reactor.getEffluent`. The 2026-03-02 fix is the only thing keeping the older shape alive in production. If `reactor.getEffluent` ever returns a 3-stream array and settler should consume `inlet=0` specifically, the current `raw[0]` selector works by accident &mdash; it picks the first envelope regardless of inlet number. Open question whether to make the selection inlet-aware.
+
+### Stateful telemetry &mdash; no decay / no TTL
+
+The MeasurementContainer holds the last-known value of every re-emitted measurement forever. If a child stops publishing, the stale value persists on Port 1 indefinitely. There is no TTL, no `data.clear-measurement` topic, and no health flag like `rotatingMachine`'s `predictionQuality`. Open question.
+
+---
+
+## Open questions (tracked)
+
+| Question | Where it lives |
+|:---|:---|
+| Filter `_connectMeasurement` by asset-type at register time? | Internal &mdash; not yet ticketed |
+| Multi-reactor upstream support &mdash; teardown ordering, listener detach | Internal |
+| Flow-balance warning when `F_s` clamp fires | Internal |
+| Inlet-aware selection in `_connectReactor` shape handling | Internal |
+| Measurement TTL / staleness flag | Internal |
+| Production-grade example flows (Tier 1 / 2 / 3) | `.agents/improvements/IMPROVEMENTS_BACKLOG.md` |
+| Output manifest + degraded-state tests | `.claude/rules/output-coverage.md` (platform-wide rule) |
+| Editor colour cleanup (`#e4a363` &rarr; `#50a8d9`) | `.claude/rules/node-red-flow-layout.md` §16 |
+
+---
+
+## Migration notes
+
+> [!NOTE]
+> Pending full node review (2026-05). No structural migrations have been performed on settler since the AssetResolver refactor of rotatingMachine; the notes below document the one historical fix on record.
+
+### From pre-2026-03-02 `_connectReactor`
+
+Before 2026-03-02 `_connectReactor` assumed `reactor.getEffluent` always returned an array, and indexed `[0]` unconditionally. After the reactor refactor, `getEffluent` returns a single envelope &mdash; pre-fix settler would crash with `Cannot read properties of undefined (reading 'payload')`. The fix:
+
+```js
+const raw = this.upstreamReactor.getEffluent;
+const effluent = Array.isArray(raw) ? raw[0] : raw;
+```
+
+If you maintain a fork of settler from before that date, port this guard.
+
+### From topic-aliased payloads
+
+Both `influent` and `setInfluent` are accepted as aliases for `data.influent`. A one-time deprecation warning fires the first time each alias is seen. Tracked for removal; use the canonical `data.influent` in new flows.
+
+---
+
+## Related pages
+
+| Page | Why |
+|:---|:---|
+| [Home](Home) | Intuitive overview |
+| [Reference &mdash; Contracts](Reference-Contracts) | Topic + config + child filters |
+| [Reference &mdash; Architecture](Reference-Architecture) | Code map, reactor &harr; settler wiring, mass-balance math |
+| [Reference &mdash; Examples](Reference-Examples) | Shipped flows + the TODO list for production-grade demos |
+| [reactor &mdash; Limitations](https://gitea.wbd-rd.nl/RnD/reactor/wiki/Reference-Limitations) | The upstream parent &mdash; effluent shape contract |
+| [EVOLV &mdash; output-coverage rule](https://gitea.wbd-rd.nl/RnD/EVOLV/src/branch/development/.claude/rules/output-coverage.md) | Platform-wide output-coverage requirement |

wiki/_Sidebar.md

@@ -0,0 +1,19 @@
+### settler
+
+- [Home](Home)
+
+**Reference**
+
+- [Contracts](Reference-Contracts)
+- [Architecture](Reference-Architecture)
+- [Examples](Reference-Examples)
+- [Limitations](Reference-Limitations)
+
+**Related**
+
+- [EVOLV master wiki](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Home)
+- [reactor wiki](https://gitea.wbd-rd.nl/RnD/reactor/wiki/Home)
+- [rotatingMachine wiki](https://gitea.wbd-rd.nl/RnD/rotatingMachine/wiki/Home)
+- [Topology Patterns](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topology-Patterns)
+- [Topic Conventions](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Topic-Conventions)
+- [Telemetry](https://gitea.wbd-rd.nl/RnD/EVOLV/wiki/Telemetry)