docs: cover breaker-aware sizing, max length, socket minimum, manual entry

docs/cable-sizing-module.md

@@ -76,14 +76,50 @@ cell, nothing crashes, no data is affected, and the rest of the app
 (including manual cable-field editing) is completely unaffected - the
 module's actual logic and persistence never depend on this column key.
 
-## How a suggestion is applied
+## Feature overview
 
-The module never writes to `circuits` directly. The modal's "Empfehlung
-übernehmen" button calls the **existing, unmodified** frontend helper:
+- **Calculate a recommendation**: laying method, insulation, conductor
+  material, ambient temperature, grouping, cos phi and max voltage drop -
+  same VDE 0298-4 reference-method model as the sibling Kabelliste tool
+  (see Verification status below).
+- **Breaker-aware sizing**: if the circuit already has a protection device
+  (`circuit.protectionDevice`), the cross-section is selected against
+  `designCurrentA = max(operatingCurrentA, protectionDevice.ratedCurrentA)`,
+  not the load current alone - the standard `In <= Iz` rule (a breaker only
+  trips at its own rated current, so a cable sized for the actual load
+  alone could overheat under sustained current below that threshold). If no
+  cross-section can cover an oversized breaker, that is reported as the
+  limiting factor by name, not a generic capacity error.
+- **Maximum length for the voltage-drop limit**: each cross-section option
+  also reports the longest single run that still meets the requested
+  `maxVoltageDropPercent` at the given load - the inverse of the
+  voltage-drop check, shown for the recommended cross-section.
+- **Practical minimum for socket circuits**: `single_phase`-category
+  circuits are raised to at least 2.5 mm² if the calculation alone would
+  recommend less - see the dedicated note under Verification status. Never
+  lowers a calculation that already needs more.
+- **Manual entry, always available**: the modal has a plain text Kabeltyp/
+  Querschnitt field. Running a calculation pre-fills it as a suggestion,
+  but the field is the single source of truth for what gets applied, and
+  stays freely editable - satisfying
+  `docs/spec/06-future-sizing-and-calculations.md`'s explicit requirement
+  that "users must remain able to manually override suggestions" without
+  requiring a calculation to have been run first. A non-blocking warning
+  appears if the typed value is not a standard cross-section, is smaller
+  than the last calculation, or is below the practical minimum above -
+  informational only, never forced, matching the same spec doc's "shown as
+  a warning or status indicator, not as an automatic forced change."
+
+## How a suggestion or manual entry is applied
+
+The module never writes to `circuits` directly. The modal's "Übernehmen"
+button calls the **existing, unmodified** frontend helper with whatever is
+currently in the Kabeltyp/Querschnitt fields, calculated or hand-typed:
 
 ```ts
 updateCircuitById(projectId, expectedRevision, circuitId, {
   cableCrossSection: "4 mm²",
+  cableType: "NYM-J 3x2.5",
   cableLength: 30,
 });
 ```
@@ -94,10 +130,8 @@ cell edits. This means:
 - optimistic concurrency (`expectedRevision`) is respected automatically
 - the change appears in the project's revision history and is undoable/
   redoable exactly like a manual edit
-- manually typing a value into the `cableCrossSection` cell keeps working
-  unchanged - the module only adds a small calculator trigger next to the
-  cell, per `docs/spec/06-future-sizing-and-calculations.md`'s explicit
-  requirement that "users must remain able to manually override suggestions"
+- nothing is ever written automatically - calculating only fills the modal's
+  own fields, applying is always an explicit, separate click
 
 ## API contract
 
@@ -119,6 +153,8 @@ cell edits. This means:
   "maxVoltageDropPercent": 3,
   "harmonicNeutralLoad": "none",   // "none" | "15to33Percent" | "over33Percent", three-phase only
   "existingProtectionRatedCurrentA": 16,  // optional, from circuit.protectionDevice
+  "circuitCategory": "single_phase",      // optional, from the circuit's section.category -
+                                            // enables the practical-minimum convention below
   "context": { "projectId": "...", "circuitId": "...", "equipmentIdentifier": "-1F1.1" }
 }
 ```
@@ -149,6 +185,15 @@ recommended cross-section's corrected capacity) is a **simplified** `In <=
 Iz` check only - it is not a full IEC 60364-4-43 overload (`I2 <= 1.45 x
 Iz`) or short-circuit withstand check.
 
+`PRACTICAL_MINIMUM_CROSS_SECTION_MM2` (2.5 mm² for `single_phase`) is
+**not** a verified norm value at all - it is a named planning convention,
+sourced directly from this project's own
+`docs/spec/06-future-sizing-and-calculations.md` ("Standard Single-Phase
+Circuits ... usually use ... cable cross-section: 2.5 mm²"), applied as a
+floor on top of the calculated recommendation. It intentionally only
+covers the one category and one convention that document already states;
+it is not a general substitute for norm-compliant calculation.
+
 ## Relationship to the project's own future-sizing spec
 
 `docs/spec/06-future-sizing-and-calculations.md` separately describes simple
@@ -177,8 +222,22 @@ app for now", per the intent of this proposal.
 
 ## Local testing
 
-Deployed and manually exercised on an internal test host at
-`http://192.168.0.133:3220` (a fork of this repository's `main` branch, not
-pushed anywhere). `npm test`, `npm run build:api`, `npm run build:web` and
-`npm run typecheck:scripts` all pass with this module included; see the
-accompanying diff/branch for the exact commit.
+Deployed and manually exercised end-to-end on an internal test host at
+`http://192.168.0.133:3220` (own docker deployment, own subnet/ports to
+avoid clashing with ~50 other containers on that host - see the two
+commits marked "Local-only" in this branch, which are not part of this
+proposal and should not be carried over if it is ever proposed upstream).
+Exercised against seeded real project/circuit data created through the
+actual command API (not direct DB writes), including a deliberately long
+(85 m) circuit to trigger the voltage-drop-critical path.
+
+`npm test`, `npm run build:api`, `npm run build:web` and
+`npm run typecheck:scripts` all pass with this module included at every
+commit in this branch.
+
+This branch (`feature/cable-sizing-module`) is pushed to a mirror of this
+repository under this homelab's own Forgejo instance, not to
+`git.jappel.io` - no write access to the upstream repository was available
+or used. See the branch's commit history for the incremental history of
+this module, including fixes made during manual testing (trigger column,
+icon rendering, breaker-aware sizing).