diff --git a/.project/concepts/app-architecture/_debt.md b/.project/concepts/app-architecture/_debt.md
new file mode 100644
index 0000000..59c4409
--- /dev/null
+++ b/.project/concepts/app-architecture/_debt.md
@@ -0,0 +1,7 @@
+# Doc-debt — app-architecture
+
+> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
+> One block = one "big change": `why` + `files` + `verify` (leaves to review).
+
+## Raw markers (consolidate into blocks, then delete)
+- TOUCHED src/shared/context/FestipodDataContext.tsx @2026-08-17 (session 0b064e8b-1717-421f-a20e-a4318ad217b1)
diff --git a/.project/concepts/data-layer/_debt.md b/.project/concepts/data-layer/_debt.md
new file mode 100644
index 0000000..f4ad808
--- /dev/null
+++ b/.project/concepts/data-layer/_debt.md
@@ -0,0 +1,9 @@
+# Doc-debt — data-layer
+
+> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
+> One block = one "big change": `why` + `files` + `verify` (leaves to review).
+
+## Raw markers (consolidate into blocks, then delete)
+- TOUCHED src/shared/shapes/shex/festipodShapes.shex @2026-08-17 (session 0b064e8b-1717-421f-a20e-a4318ad217b1)
+- TOUCHED src/shared/context/FestipodDataContext.tsx @2026-08-17 (session 0b064e8b-1717-421f-a20e-a4318ad217b1)
+- TOUCHED src/shared/data/shapeAdapters.ts @2026-08-17 (session 0b064e8b-1717-421f-a20e-a4318ad217b1)
diff --git a/.project/concepts/data-layer/contract_polyfill-surface.md b/.project/concepts/data-layer/polyfill-surface/contract_polyfill-surface.md
similarity index 100%
rename from .project/concepts/data-layer/contract_polyfill-surface.md
rename to .project/concepts/data-layer/polyfill-surface/contract_polyfill-surface.md
diff --git a/.project/concepts/tech-stack/_debt.md b/.project/concepts/tech-stack/_debt.md
new file mode 100644
index 0000000..941b81d
--- /dev/null
+++ b/.project/concepts/tech-stack/_debt.md
@@ -0,0 +1,7 @@
+# Doc-debt — tech-stack
+
+> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
+> One block = one "big change": `why` + `files` + `verify` (leaves to review).
+
+## Raw markers (consolidate into blocks, then delete)
+- TOUCHED package.json @2026-08-17 (session 0b064e8b-1717-421f-a20e-a4318ad217b1)
diff --git a/src/shared/context/FestipodDataContext.tsx b/src/shared/context/FestipodDataContext.tsx
index 3c5aecf..a9f17d8 100644
--- a/src/shared/context/FestipodDataContext.tsx
+++ b/src/shared/context/FestipodDataContext.tsx
@@ -1178,6 +1178,12 @@ function useNgData(): FestipodDataContextValue {
     await openDocumentInbox(eventGraph);
     const eventId = await writeEntity(eventGraph, ENTITY_TYPE.event, {
       title: str(event.title), description: str(event.description), date: str(event.date),
+      // `date` is the human LABEL the form composed; these four are the machine
+      // values it collected, written UNALTERED as the form's own ISO forms
+      // (`YYYY-MM-DD`, `HH:MM`). They are stored alongside the label, never
+      // derived from it — the label is display text and cannot be parsed back.
+      startDate: str(event.startDate), endDate: str(event.endDate),
+      startTime: str(event.startTime), endTime: str(event.endTime),
       location: str(event.location), distance: flt(event.distance),
       // No host notion: the creator merely SIGNALS a public event and is NOT
       // obliged to participate, so the count starts at 0 (the owner-materializer
@@ -1231,6 +1237,14 @@ function useNgData(): FestipodDataContextValue {
     if (updates.title !== undefined) persists.push(updateEntityField(graph, id, 'title', str(updates.title)));
     if (updates.description !== undefined) persists.push(updateEntityField(graph, id, 'description', str(updates.description)));
     if (updates.date !== undefined) persists.push(updateEntityField(graph, id, 'date', str(updates.date)));
+    // The machine dates/times travel with the label, not instead of it. A field
+    // arriving as `''` (the form's empty date input) CLEARS the triple rather than
+    // leaving a stale value behind — that is `updateEntityField`'s empty handling,
+    // and it is the right reading here: the user emptied the input.
+    if (updates.startDate !== undefined) persists.push(updateEntityField(graph, id, 'startDate', str(updates.startDate)));
+    if (updates.endDate !== undefined) persists.push(updateEntityField(graph, id, 'endDate', str(updates.endDate)));
+    if (updates.startTime !== undefined) persists.push(updateEntityField(graph, id, 'startTime', str(updates.startTime)));
+    if (updates.endTime !== undefined) persists.push(updateEntityField(graph, id, 'endTime', str(updates.endTime)));
     if (updates.location !== undefined) persists.push(updateEntityField(graph, id, 'location', str(updates.location)));
     if (updates.distance !== undefined) persists.push(updateEntityField(graph, id, 'distance', flt(updates.distance)));
     await Promise.all(persists).catch(err => console.error(`${logPrefix} persist event update failed:`, err));
diff --git a/src/shared/data/shapeAdapters.ts b/src/shared/data/shapeAdapters.ts
index f1cbf6d..24f9d82 100644
--- a/src/shared/data/shapeAdapters.ts
+++ b/src/shared/data/shapeAdapters.ts
@@ -37,6 +37,15 @@ export function adaptEvent(s: UnionSubject): FpEventData {
     title: one(s, 'title'),
     description: one(s, 'description'),
     date: one(s, 'date'),
+    // The four machine values, read back exactly as stored (`YYYY-MM-DD`, `HH:MM`).
+    // `undefined` — not `''` — when the triple is absent: the app type declares them
+    // optional and the screens branch on their PRESENCE (`event.startTime && …`), so
+    // an event written before these fields existed reads as an event without them
+    // rather than one whose dates are blank strings.
+    startDate: one(s, 'startDate') || undefined,
+    endDate: one(s, 'endDate') || undefined,
+    startTime: one(s, 'startTime') || undefined,
+    endTime: one(s, 'endTime') || undefined,
     location: one(s, 'location'),
     distance: s.props[`${FP}distance`] ? num(s, 'distance') : undefined,
     participantCount: num(s, 'participantCount'),
diff --git a/src/shared/shapes/orm/festipodShapes.schema.ts b/src/shared/shapes/orm/festipodShapes.schema.ts
index cdbcdc8..bc1e313 100644
--- a/src/shared/shapes/orm/festipodShapes.schema.ts
+++ b/src/shared/shapes/orm/festipodShapes.schema.ts
@@ -54,6 +54,50 @@ export const festipodShapesSchema = {
         iri: "http://festipod.org/date",
         readablePredicate: "date",
       },
+      {
+        dataTypes: [
+          {
+            valType: "string",
+          },
+        ],
+        maxCardinality: 1,
+        minCardinality: 0,
+        iri: "http://festipod.org/startDate",
+        readablePredicate: "startDate",
+      },
+      {
+        dataTypes: [
+          {
+            valType: "string",
+          },
+        ],
+        maxCardinality: 1,
+        minCardinality: 0,
+        iri: "http://festipod.org/endDate",
+        readablePredicate: "endDate",
+      },
+      {
+        dataTypes: [
+          {
+            valType: "string",
+          },
+        ],
+        maxCardinality: 1,
+        minCardinality: 0,
+        iri: "http://festipod.org/startTime",
+        readablePredicate: "startTime",
+      },
+      {
+        dataTypes: [
+          {
+            valType: "string",
+          },
+        ],
+        maxCardinality: 1,
+        minCardinality: 0,
+        iri: "http://festipod.org/endTime",
+        readablePredicate: "endTime",
+      },
       {
         dataTypes: [
           {
diff --git a/src/shared/shapes/orm/festipodShapes.typings.ts b/src/shared/shapes/orm/festipodShapes.typings.ts
index c449347..20f09f5 100644
--- a/src/shared/shapes/orm/festipodShapes.typings.ts
+++ b/src/shared/shapes/orm/festipodShapes.typings.ts
@@ -40,6 +40,30 @@ export interface Event {
    * Original IRI: http://festipod.org/date
    */
   date: string;
+  /**
+   * The day the event starts, as the ISO calendar date the form collects (YYYY-MM-DD) — stored unaltered, never derived from fp:date
+   *
+   * Original IRI: http://festipod.org/startDate
+   */
+  startDate?: string;
+  /**
+   * The day the event ends, as an ISO calendar date (YYYY-MM-DD); absent for a single-day event
+   *
+   * Original IRI: http://festipod.org/endDate
+   */
+  endDate?: string;
+  /**
+   * The time of day the event starts, as the form collects it (HH:MM)
+   *
+   * Original IRI: http://festipod.org/startTime
+   */
+  startTime?: string;
+  /**
+   * The time of day the event ends (HH:MM)
+   *
+   * Original IRI: http://festipod.org/endTime
+   */
+  endTime?: string;
   /**
    * The location of the event
    *
diff --git a/src/shared/shapes/shex/festipodShapes.shex b/src/shared/shapes/shex/festipodShapes.shex
index 5f94c65..9a92d9b 100644
--- a/src/shared/shapes/shex/festipodShapes.shex
+++ b/src/shared/shapes/shex/festipodShapes.shex
@@ -10,6 +10,14 @@ fp:Event {
     // rdfs:comment "A description of the event" ;
   fp:date xsd:string
     // rdfs:comment "The display date of the event (e.g. 'Lun. 16 - Ven. 20 fév.')" ;
+  fp:startDate xsd:string ?
+    // rdfs:comment "The day the event starts, as the ISO calendar date the form collects (YYYY-MM-DD) — stored unaltered, never derived from fp:date" ;
+  fp:endDate xsd:string ?
+    // rdfs:comment "The day the event ends, as an ISO calendar date (YYYY-MM-DD); absent for a single-day event" ;
+  fp:startTime xsd:string ?
+    // rdfs:comment "The time of day the event starts, as the form collects it (HH:MM)" ;
+  fp:endTime xsd:string ?
+    // rdfs:comment "The time of day the event ends (HH:MM)" ;
   fp:location xsd:string
     // rdfs:comment "The location of the event" ;
   fp:distance xsd:float ?