panel: clausal chain editor (WHEN/AT/EVERY + AND/OR/THEN)

Multi-record clausal programs are now editable end-to-end. A chain
spans N consecutive slots — head (WHEN/AT/EVERY) + zero-or-more
AND/OR condition records + one-or-more THEN action records — so
"editing" means rewriting the whole run, validating that any
expansion doesn't trample adjacent programs, and clearing any old
slots when the chain shrinks.

H1 — backend:

* programs/get for chains now returns chain_members[] with each
  member's slot + role + raw fields. The editor uses this to seed
  one editable form-row per slot.
* New programs/chain/write command: takes head_slot + head dict +
  conditions[] + actions[], does N sequential download_program
  calls, then clears any old chain slots that fell outside the new
  range. Validates:
    - head_slot + new_len doesn't extend past slot 1500
    - any expansion-into slot not already part of THIS chain is FREE
      (anti-trample: refuse rather than overwrite an adjacent program)
    - at least one THEN action present (empty chain rejected)
  Updates coordinator.data.programs immediately so subsequent list
  calls reflect the edit before the next poll.

H2 — TS helpers:

* AND-record encoding mirrors compact-form cond family bytes
  (0x04 ZONE / 0x08 CTRL / 0x0C TIME / 0x00 OTHER + 0x10+ SEC) but
  with a slightly different bit layout: the family byte lives at
  fields.cond & 0xFF (disk byte 1) and the instance at
  (fields.cond2 >> 8) & 0xFF (disk byte 3). The selector bit is
  family's bit 0x02 instead of cond's 0x0200. decodeAndCondition /
  encodeAndCondition handle both directions; round-trip exact.
* isStructuredAnd helper detects records with OP > 0 (TEMP > N
  comparisons etc.); those render read-only in the chain editor
  with a warning banner.
* emptyAndRecord / emptyOrRecord / emptyThenRecord helpers for
  the add-condition / add-action buttons.

H3 — chain editor UI:

* New _chainDraft state (parallel to _editingDraft for compact form)
  with head + conditions[] + actions[] arrays. Mutation helpers
  preserve immutability via array-copy-then-patch.
* "Edit" button on chain detail now opens the chain editor instead
  of returning early (previous read-only behaviour).
* Three sub-renderers: trigger section dispatches on prog_type
  (WHEN→event-id builder reusing the EVENT helpers, AT→time+days
  reusing TIMED layout, EVERY→single seconds input that packs into
  cond+cond2), conditions section with per-row add/remove (separate
  + AND IF and + OR IF buttons in the legend), actions section with
  per-row add/remove (+ THEN button; at least one action enforced).
* Structured-OP AND records render with an explanatory read-only
  banner and a × button to drop the row entirely — preserves the
  data when the user doesn't touch it, lets them remove it cleanly
  when they want to.
* Each row picks objects via _bucketWithPreserve so out-of-range
  zone/unit/area indices stay safe.

5 new HA integration tests:
* get-chain returns chain_members with correct roles + raw fields
* chain/write in-place rewrite preserves footprint, updates bytes
* chain/write shrink clears the trailing old slots
* chain/write refuses to trample an adjacent program on expansion
* chain/write rejects zero-actions submission

Live screenshot 11-chain-editor.png: state injection into the side
panel (real panel has no chains) shows the editor rendering a sample
WHEN zone-state → AND IF unit ON → 2x THEN action chain with every
control populated and functional.

Full suite: 653 passed, 1 skipped (up from 648, 5 new chain tests).
Frontend bundle: 82 KB minified (up from 63 KB).

custom_components/omni_pca/frontend/src/omni-panel-programs.ts

@@ -25,8 +25,12 @@ import {
   MONTH_NAMES,
   NamedObject,
   ObjectListResponse,
+  PROGRAM_TYPE_AT,
   PROGRAM_TYPE_EVENT,
+  PROGRAM_TYPE_EVERY,
+  PROGRAM_TYPE_OR,
   PROGRAM_TYPE_TIMED,
+  PROGRAM_TYPE_WHEN,
   PROGRAM_TYPE_YEARLY,
   ProgramDetail,
   ProgramFields,
@@ -34,11 +38,17 @@ import {
   ProgramRow,
   SECURITY_MODE_NAMES,
   commandOptionFor,
+  decodeAndCondition,
   decodeCondition,
   decodeEventId,
+  emptyAndRecord,
+  emptyOrRecord,
+  emptyThenRecord,
+  encodeAndCondition,
   encodeCondition,
   encodeEventId,
   eventIdFromFields,
+  isStructuredAnd,
   packEventIdIntoFields,
 } from "./types.js";
 
@@ -100,6 +110,18 @@ export class OmniPanelPrograms extends LitElement {
   // omni_pca/programs/write websocket, Cancel discards.
   @state() private _editingDraft: ProgramFields | null = null;
   @state() private _objects: ObjectListResponse | null = null;
+  // Separate edit state for clausal chains. Set when the user clicks
+  // "Edit chain"; null otherwise. Head + conditions + actions are kept
+  // as parallel arrays so add/remove operations on a specific list
+  // don't churn the others. ``headSlot`` is the chain's anchor; the
+  // backend writes the new chain into [headSlot, headSlot+len) and
+  // clears any old slots beyond.
+  @state() private _chainDraft: {
+    headSlot: number;
+    head: ProgramFields;
+    conditions: ProgramFields[];
+    actions: ProgramFields[];
+  } | null = null;
 
   private _refreshTimer: number | null = null;
 
@@ -324,17 +346,18 @@ export class OmniPanelPrograms extends LitElement {
   }
 
   private async _beginEdit(): Promise<void> {
-    if (!this._detail || this._detail.kind !== "compact") return;
-    // The frontend supports editing compact-form TIMED / EVENT / YEARLY
-    // programs. Other compact types (REMARK) and clausal chains remain
-    // read-only — the editor pathway returns early without seeding a
-    // draft so the read-only view stays visible.
-    if (!EDITABLE_PROG_TYPES.has(this._detail.trigger_type)) return;
+    if (!this._detail) return;
     await this._ensureObjectsLoaded();
     if (!this._entryId) return;
-    // The detail response now carries raw fields directly. If they're
-    // missing (panel returned only tokens) we fall back to sensible
-    // defaults so the form at least opens — better than a hard error.
+    if (this._detail.kind === "chain") {
+      this._beginChainEdit();
+      return;
+    }
+    // The frontend supports editing compact-form TIMED / EVENT / YEARLY
+    // programs. Other compact types (REMARK) remain read-only — the
+    // editor pathway returns early without seeding a draft so the
+    // read-only view stays visible.
+    if (!EDITABLE_PROG_TYPES.has(this._detail.trigger_type)) return;
     const fields = this._detail.fields ?? this._defaultFieldsForType(
       this._detail.trigger_type,
     );
@@ -343,6 +366,110 @@ export class OmniPanelPrograms extends LitElement {
     this._stopRefreshTimer();
   }
 
+  private _beginChainEdit(): void {
+    if (!this._detail || !this._detail.chain_members) return;
+    const members = this._detail.chain_members;
+    const head = members.find((m) => m.role === "head");
+    if (!head) return;
+    this._chainDraft = {
+      headSlot: head.slot,
+      head: { ...head.fields },
+      conditions: members
+        .filter((m) => m.role === "condition")
+        .map((m) => ({ ...m.fields })),
+      actions: members
+        .filter((m) => m.role === "action")
+        .map((m) => ({ ...m.fields })),
+    };
+    this._stopRefreshTimer();
+  }
+
+  private _cancelChainEdit(): void {
+    this._chainDraft = null;
+    this._startRefreshTimer();
+  }
+
+  private async _saveChainDraft(): Promise<void> {
+    if (!this._chainDraft || !this._entryId) return;
+    this._writeFeedback = "saving chain…";
+    try {
+      await this.hass.connection.sendMessagePromise({
+        type: "omni_pca/programs/chain/write",
+        entry_id: this._entryId,
+        head_slot: this._chainDraft.headSlot,
+        head: this._chainDraft.head,
+        conditions: this._chainDraft.conditions,
+        actions: this._chainDraft.actions,
+      });
+      this._writeFeedback = `saved chain @ slot ${this._chainDraft.headSlot}`;
+      const headSlot = this._chainDraft.headSlot;
+      this._chainDraft = null;
+      this._startRefreshTimer();
+      await this._loadList();
+      await this._loadDetail(headSlot);
+    } catch (err) {
+      const m = err instanceof Error ? err.message : String(err);
+      this._writeFeedback = `error: ${m}`;
+    }
+    setTimeout(() => { this._writeFeedback = null; }, 4000);
+  }
+
+  // ---- chain draft mutation helpers ---------------------------------
+
+  private _patchChainHead(patch: Partial<ProgramFields>): void {
+    if (!this._chainDraft) return;
+    this._chainDraft = {
+      ...this._chainDraft,
+      head: { ...this._chainDraft.head, ...patch },
+    };
+  }
+
+  private _patchChainCondition(idx: number, patch: Partial<ProgramFields>): void {
+    if (!this._chainDraft) return;
+    const conds = [...this._chainDraft.conditions];
+    conds[idx] = { ...conds[idx], ...patch };
+    this._chainDraft = { ...this._chainDraft, conditions: conds };
+  }
+
+  private _addChainCondition(asOr: boolean = false): void {
+    if (!this._chainDraft) return;
+    const fresh = asOr ? emptyOrRecord() : emptyAndRecord();
+    this._chainDraft = {
+      ...this._chainDraft,
+      conditions: [...this._chainDraft.conditions, fresh],
+    };
+  }
+
+  private _removeChainCondition(idx: number): void {
+    if (!this._chainDraft) return;
+    const conds = this._chainDraft.conditions.filter((_, i) => i !== idx);
+    this._chainDraft = { ...this._chainDraft, conditions: conds };
+  }
+
+  private _patchChainAction(idx: number, patch: Partial<ProgramFields>): void {
+    if (!this._chainDraft) return;
+    const actions = [...this._chainDraft.actions];
+    actions[idx] = { ...actions[idx], ...patch };
+    this._chainDraft = { ...this._chainDraft, actions: actions };
+  }
+
+  private _addChainAction(): void {
+    if (!this._chainDraft) return;
+    const firstUnit = this._objects?.units?.[0]?.index ?? 1;
+    this._chainDraft = {
+      ...this._chainDraft,
+      actions: [...this._chainDraft.actions, emptyThenRecord(firstUnit)],
+    };
+  }
+
+  private _removeChainAction(idx: number): void {
+    if (!this._chainDraft) return;
+    // Guard: a chain must have at least one action.
+    if (this._chainDraft.actions.length <= 1) return;
+    const actions = this._chainDraft.actions.filter((_, i) => i !== idx);
+    this._chainDraft = { ...this._chainDraft, actions: actions };
+  }
+
   private _defaultFieldsForType(triggerType: string): ProgramFields | null {
     const firstUnit = this._objects?.units?.[0]?.index ?? 1;
     if (triggerType === "TIMED") {
@@ -767,6 +894,9 @@ export class OmniPanelPrograms extends LitElement {
     if (this._editingDraft !== null) {
       return this._renderEditor(d);
     }
+    if (this._chainDraft !== null) {
+      return this._renderChainEditor(d);
+    }
     return html`
       <aside class="detail">
         <header>
@@ -785,7 +915,9 @@ export class OmniPanelPrograms extends LitElement {
             class="fire"
             @click=${() => this._fireProgram(d.slot)}
           >▶ Fire now</button>
-          ${d.kind === "compact" && EDITABLE_PROG_TYPES.has(d.trigger_type) ? html`
+          ${
+            (d.kind === "compact" && EDITABLE_PROG_TYPES.has(d.trigger_type))
+            || d.kind === "chain" ? html`
             <button
               type="button"
               class="secondary"
@@ -1378,6 +1510,587 @@ export class OmniPanelPrograms extends LitElement {
       </label>`;
   }
 
+  // ---- clausal chain editor -----------------------------------------
+
+  private _renderChainEditor(d: ProgramDetail): TemplateResult {
+    const draft = this._chainDraft!;
+    return html`
+      <aside class="detail editor">
+        <header>
+          <div>
+            <span class="trigger-badge trigger-${d.trigger_type.toLowerCase()}">
+              EDIT • ${d.trigger_type}
+            </span>
+            <span class="slot">head @ slot #${draft.headSlot}</span>
+          </div>
+          <button type="button" class="close" @click=${this._cancelChainEdit}>×</button>
+        </header>
+
+        <div class="editor-body">
+          ${this._renderChainHeadSection(draft.head)}
+          ${this._renderChainConditionsSection(draft.conditions)}
+          ${this._renderChainActionsSection(draft.actions)}
+          <div class="chain-meta">
+            Chain will occupy <strong>${1 + draft.conditions.length + draft.actions.length}</strong>
+            consecutive slots starting at #${draft.headSlot}.
+          </div>
+        </div>
+
+        <footer>
+          <button type="button" class="primary" @click=${this._saveChainDraft}>
+            Save chain
+          </button>
+          <button type="button" class="secondary" @click=${this._cancelChainEdit}>
+            Cancel
+          </button>
+          ${this._writeFeedback ? html`
+            <span class="fire-feedback">${this._writeFeedback}</span>` : ""}
+        </footer>
+      </aside>
+    `;
+  }
+
+  private _renderChainHeadSection(head: ProgramFields): TemplateResult {
+    // Reuse the existing trigger-section renderers from the compact-form
+    // editor — head records share the same field semantics as their
+    // compact counterparts (AT = TIMED, WHEN = EVENT, EVERY uses
+    // cond/cond2 for interval). The renderers patch via _patchDraft,
+    // which we shim to redirect to _patchChainHead while in chain mode.
+    if (head.prog_type === PROGRAM_TYPE_WHEN) {
+      return this._renderEventTriggerChain(head);
+    }
+    if (head.prog_type === PROGRAM_TYPE_AT) {
+      return this._renderTimedTriggerChain(head);
+    }
+    if (head.prog_type === PROGRAM_TYPE_EVERY) {
+      return this._renderEveryTriggerChain(head);
+    }
+    return html`
+      <div class="conditions-readonly">
+        Editing trigger type ${head.prog_type} (chain head) is not supported.
+      </div>`;
+  }
+
+  private _renderTimedTriggerChain(head: ProgramFields): TemplateResult {
+    // Same fields as TIMED compact: hour/minute/days.
+    return html`
+      <fieldset>
+        <legend>AT (trigger)</legend>
+        <div class="row">
+          <label>
+            Hour
+            <input type="number" min="0" max="23"
+              .value=${String(head.hour ?? 0)}
+              @input=${(e: Event) => this._patchChainHead({
+                hour: parseInt((e.target as HTMLInputElement).value, 10) || 0,
+              })}
+            />
+          </label>
+          <span class="time-colon">:</span>
+          <label>
+            Minute
+            <input type="number" min="0" max="59"
+              .value=${String(head.minute ?? 0)}
+              @input=${(e: Event) => this._patchChainHead({
+                minute: parseInt((e.target as HTMLInputElement).value, 10) || 0,
+              })}
+            />
+          </label>
+        </div>
+        <div class="days-row">
+          ${DAY_BITS.map((d) => {
+            const active = ((head.days ?? 0) & d.bit) !== 0;
+            return html`
+              <button type="button"
+                class="day-toggle ${active ? "active" : ""}"
+                @click=${() => this._patchChainHead({
+                  days: (head.days ?? 0) ^ d.bit,
+                })}
+              >${d.label}</button>`;
+          })}
+        </div>
+      </fieldset>
+    `;
+  }
+
+  private _renderEventTriggerChain(head: ProgramFields): TemplateResult {
+    // WHEN heads use the same event-id packing as EVENT compact-form:
+    // month/day bytes carry (event_id >> 8) and (event_id & 0xFF).
+    const eventId = ((head.month ?? 0) << 8) | (head.day ?? 0);
+    const decoded = decodeEventId(eventId);
+    const setEvent = (e: DecodedEvent) => {
+      const id = encodeEventId(e);
+      this._patchChainHead({
+        month: (id >> 8) & 0xFF,
+        day: id & 0xFF,
+      });
+    };
+    return html`
+      <fieldset>
+        <legend>WHEN (trigger event)</legend>
+        <label class="block">
+          Category
+          <select @change=${(e: Event) => {
+            const cat = (e.target as HTMLSelectElement).value as EventCategory;
+            if (cat === "button") {
+              const fb = this._objects?.buttons?.[0]?.index ?? 1;
+              setEvent({ category: "button", button: fb });
+            } else if (cat === "zone") {
+              const fz = this._objects?.zones?.[0]?.index ?? 1;
+              setEvent({ category: "zone", zone: fz, zoneState: 1 });
+            } else if (cat === "unit") {
+              const fu = this._objects?.units?.[0]?.index ?? 1;
+              setEvent({ category: "unit", unit: fu, unitOn: true });
+            } else if (cat === "fixed") {
+              setEvent({ category: "fixed", fixedId: 772 });
+            }
+          }}>
+            <option value="button" ?selected=${decoded.category === "button"}>Button press</option>
+            <option value="zone" ?selected=${decoded.category === "zone"}>Zone state change</option>
+            <option value="unit" ?selected=${decoded.category === "unit"}>Unit state change</option>
+            <option value="fixed" ?selected=${decoded.category === "fixed"}>Fixed (phone / AC)</option>
+            ${decoded.category === "raw" ? html`
+              <option value="raw" selected>Raw 0x${eventId.toString(16).padStart(4, "0")}</option>` : ""}
+          </select>
+        </label>
+        ${this._renderChainEventSubfields(decoded, setEvent)}
+      </fieldset>
+    `;
+  }
+
+  private _renderChainEventSubfields(
+    decoded: DecodedEvent, setEvent: (e: DecodedEvent) => void,
+  ): TemplateResult {
+    if (decoded.category === "button") {
+      const buttons = this._bucketWithPreserve(
+        this._objects?.buttons ?? null, "button", decoded.button ?? 0,
+      );
+      return html`
+        <label class="block">
+          Button
+          <select @change=${(e: Event) => setEvent({
+            category: "button",
+            button: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${buttons.map((b) => html`
+              <option .value=${String(b.index)}
+                      ?selected=${b.index === decoded.button}>
+                #${b.index} ${b.name}
+              </option>
+            `)}
+          </select>
+        </label>`;
+    }
+    if (decoded.category === "zone") {
+      const zones = this._bucketWithPreserve(
+        this._objects?.zones ?? null, "zone", decoded.zone ?? 0,
+      );
+      return html`
+        <label class="block">
+          Zone
+          <select @change=${(e: Event) => setEvent({
+            ...decoded, category: "zone",
+            zone: parseInt((e.target as HTMLSelectElement).value, 10),
+            zoneState: decoded.zoneState ?? 1,
+          })}>
+            ${zones.map((z) => html`
+              <option .value=${String(z.index)}
+                      ?selected=${z.index === decoded.zone}>
+                #${z.index} ${z.name}
+              </option>
+            `)}
+          </select>
+        </label>
+        <label class="block">
+          Becomes
+          <select @change=${(e: Event) => setEvent({
+            ...decoded, category: "zone",
+            zone: decoded.zone ?? 1,
+            zoneState: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            <option value="0" ?selected=${decoded.zoneState === 0}>secure</option>
+            <option value="1" ?selected=${decoded.zoneState === 1}>not ready</option>
+            <option value="2" ?selected=${decoded.zoneState === 2}>trouble</option>
+            <option value="3" ?selected=${decoded.zoneState === 3}>tamper</option>
+          </select>
+        </label>`;
+    }
+    if (decoded.category === "unit") {
+      const units = this._bucketWithPreserve(
+        this._objects?.units ?? null, "unit", decoded.unit ?? 0,
+      );
+      return html`
+        <label class="block">
+          Unit
+          <select @change=${(e: Event) => setEvent({
+            ...decoded, category: "unit",
+            unit: parseInt((e.target as HTMLSelectElement).value, 10),
+            unitOn: decoded.unitOn ?? true,
+          })}>
+            ${units.map((u) => html`
+              <option .value=${String(u.index)}
+                      ?selected=${u.index === decoded.unit}>
+                #${u.index} ${u.name}
+              </option>
+            `)}
+          </select>
+        </label>
+        <label class="block">
+          Turns
+          <select @change=${(e: Event) => setEvent({
+            ...decoded, category: "unit",
+            unit: decoded.unit ?? 1,
+            unitOn: (e.target as HTMLSelectElement).value === "1",
+          })}>
+            <option value="1" ?selected=${decoded.unitOn === true}>ON</option>
+            <option value="0" ?selected=${decoded.unitOn === false}>OFF</option>
+          </select>
+        </label>`;
+    }
+    if (decoded.category === "fixed") {
+      return html`
+        <label class="block">
+          Event
+          <select @change=${(e: Event) => setEvent({
+            category: "fixed",
+            fixedId: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${FIXED_EVENTS.map((f) => html`
+              <option .value=${String(f.id)}
+                      ?selected=${f.id === decoded.fixedId}>
+                ${f.label}
+              </option>
+            `)}
+          </select>
+        </label>`;
+    }
+    return html`<div class="conditions-readonly">Unrecognised event ID. Pick a category to redefine.</div>`;
+  }
+
+  private _renderEveryTriggerChain(head: ProgramFields): TemplateResult {
+    // EVERY's interval = ((cond & 0xFF) << 8) | ((cond2 >> 8) & 0xFF).
+    // Decode for display; the editor exposes a single "seconds" input
+    // and packs back to cond + cond2 on change.
+    const interval =
+      (((head.cond ?? 0) & 0xFF) << 8) | (((head.cond2 ?? 0) >> 8) & 0xFF);
+    return html`
+      <fieldset>
+        <legend>EVERY (interval, seconds)</legend>
+        <label class="block">
+          Seconds between fires
+          <input type="number" min="1" max="65535"
+            .value=${String(interval || 1)}
+            @input=${(e: Event) => {
+              const sec = parseInt((e.target as HTMLInputElement).value, 10);
+              if (!Number.isFinite(sec) || sec < 1) return;
+              this._patchChainHead({
+                cond: (sec >> 8) & 0xFF,
+                cond2: (sec & 0xFF) << 8,
+              });
+            }}
+          />
+        </label>
+      </fieldset>
+    `;
+  }
+
+  private _renderChainConditionsSection(conds: ProgramFields[]): TemplateResult {
+    return html`
+      <fieldset>
+        <legend>
+          Conditions (${conds.length})
+          <button type="button" class="mini-btn" @click=${() => this._addChainCondition(false)}>
+            + AND IF
+          </button>
+          <button type="button" class="mini-btn" @click=${() => this._addChainCondition(true)}>
+            + OR IF
+          </button>
+        </legend>
+        ${conds.length === 0 ? html`
+          <div class="conditions-readonly">
+            No conditions — chain fires unconditionally when triggered.
+          </div>` : ""}
+        ${conds.map((c, idx) => this._renderChainConditionRow(c, idx))}
+      </fieldset>
+    `;
+  }
+
+  private _renderChainConditionRow(
+    cond: ProgramFields, idx: number,
+  ): TemplateResult {
+    const isOr = cond.prog_type === PROGRAM_TYPE_OR;
+    if (isStructuredAnd(cond)) {
+      return html`
+        <div class="cond-slot structured-cond">
+          <div>
+            <strong>${isOr ? "OR IF" : "AND IF"}</strong> (structured comparison — read-only)
+            <button type="button" class="mini-btn danger"
+              @click=${() => this._removeChainCondition(idx)}>×</button>
+          </div>
+          <div class="conditions-readonly">
+            This condition uses a structured comparison (TEMP &gt; N etc.).
+            Editing structured-OP records is not yet supported; it's
+            preserved on save.
+          </div>
+        </div>`;
+    }
+    const decoded = decodeAndCondition(cond);
+    return html`
+      <div class="cond-slot">
+        <div class="cond-row-header">
+          <strong>${isOr ? "OR IF" : "AND IF"}</strong>
+          <button type="button" class="mini-btn danger"
+            @click=${() => this._removeChainCondition(idx)}>×</button>
+        </div>
+        ${this._renderChainCondFamily(decoded, idx)}
+      </div>`;
+  }
+
+  private _renderChainCondFamily(
+    decoded: DecodedCondition, idx: number,
+  ): TemplateResult {
+    const setFamily = (family: CondFamily) => {
+      const firstZone = this._objects?.zones?.[0]?.index ?? 1;
+      const firstUnit = this._objects?.units?.[0]?.index ?? 1;
+      const firstArea = this._objects?.areas?.[0]?.index ?? 1;
+      let next: DecodedCondition;
+      switch (family) {
+        case "none":  next = { family: "none" }; break;
+        case "misc":  next = { family: "misc", misc: 1 }; break;
+        case "zone":  next = { family: "zone", index: firstZone, active: false }; break;
+        case "unit":  next = { family: "unit", index: firstUnit, active: true }; break;
+        case "time":  next = { family: "time", index: 1, active: true }; break;
+        case "sec":   next = { family: "sec", index: firstArea, mode: 0 }; break;
+      }
+      const enc = encodeAndCondition(next);
+      this._patchChainCondition(idx, enc);
+    };
+    const setDecoded = (next: DecodedCondition) => {
+      this._patchChainCondition(idx, encodeAndCondition(next));
+    };
+    return html`
+      <label class="block">
+        Family
+        <select @change=${(e: Event) =>
+          setFamily((e.target as HTMLSelectElement).value as CondFamily)}>
+          <option value="zone" ?selected=${decoded.family === "zone"}>Zone state</option>
+          <option value="unit" ?selected=${decoded.family === "unit"}>Unit state</option>
+          <option value="sec"  ?selected=${decoded.family === "sec"}>Area in security mode</option>
+          <option value="time" ?selected=${decoded.family === "time"}>Time clock</option>
+          <option value="misc" ?selected=${decoded.family === "misc"}>Misc</option>
+        </select>
+      </label>
+      ${this._renderChainCondSubfields(decoded, setDecoded)}
+    `;
+  }
+
+  private _renderChainCondSubfields(
+    decoded: DecodedCondition, setDecoded: (d: DecodedCondition) => void,
+  ): TemplateResult {
+    if (decoded.family === "zone") {
+      const zones = this._bucketWithPreserve(
+        this._objects?.zones ?? null, "zone", decoded.index ?? 0,
+      );
+      return html`
+        <label class="block">
+          Zone
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, index: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${zones.map((z) => html`
+              <option .value=${String(z.index)} ?selected=${z.index === decoded.index}>
+                #${z.index} ${z.name}
+              </option>`)}
+          </select>
+        </label>
+        <label class="block">
+          Is
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, active: (e.target as HTMLSelectElement).value === "1",
+          })}>
+            <option value="0" ?selected=${!decoded.active}>secure</option>
+            <option value="1" ?selected=${decoded.active}>not ready</option>
+          </select>
+        </label>`;
+    }
+    if (decoded.family === "unit") {
+      const units = this._bucketWithPreserve(
+        this._objects?.units ?? null, "unit", decoded.index ?? 0,
+      );
+      return html`
+        <label class="block">
+          Unit
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, index: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${units.map((u) => html`
+              <option .value=${String(u.index)} ?selected=${u.index === decoded.index}>
+                #${u.index} ${u.name}
+              </option>`)}
+          </select>
+        </label>
+        <label class="block">
+          Is
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, active: (e.target as HTMLSelectElement).value === "1",
+          })}>
+            <option value="1" ?selected=${decoded.active}>ON</option>
+            <option value="0" ?selected=${!decoded.active}>OFF</option>
+          </select>
+        </label>`;
+    }
+    if (decoded.family === "sec") {
+      const areas = this._bucketWithPreserve(
+        this._objects?.areas ?? null, "area", decoded.index ?? 0,
+      );
+      return html`
+        <label class="block">
+          Area
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, index: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${areas.map((a) => html`
+              <option .value=${String(a.index)} ?selected=${a.index === decoded.index}>
+                #${a.index} ${a.name}
+              </option>`)}
+          </select>
+        </label>
+        <label class="block">
+          Mode
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, mode: parseInt((e.target as HTMLSelectElement).value, 10),
+          })}>
+            ${SECURITY_MODE_NAMES.map((m) => html`
+              <option .value=${String(m.value)} ?selected=${m.value === decoded.mode}>
+                ${m.label}
+              </option>`)}
+          </select>
+        </label>`;
+    }
+    if (decoded.family === "time") {
+      return html`
+        <label class="block">
+          Time clock # (1..3)
+          <input type="number" min="1" max="3"
+            .value=${String(decoded.index ?? 1)}
+            @input=${(e: Event) => {
+              const idx = parseInt((e.target as HTMLInputElement).value, 10);
+              if (Number.isFinite(idx)) setDecoded({ ...decoded, index: idx });
+            }}
+          />
+        </label>
+        <label class="block">
+          Is
+          <select @change=${(e: Event) => setDecoded({
+            ...decoded, active: (e.target as HTMLSelectElement).value === "1",
+          })}>
+            <option value="1" ?selected=${decoded.active}>enabled</option>
+            <option value="0" ?selected=${!decoded.active}>disabled</option>
+          </select>
+        </label>`;
+    }
+    // misc
+    return html`
+      <label class="block">
+        Condition
+        <select @change=${(e: Event) => setDecoded({
+          family: "misc",
+          misc: parseInt((e.target as HTMLSelectElement).value, 10),
+        })}>
+          ${MISC_CONDITIONALS.map((m) => html`
+            <option .value=${String(m.value)} ?selected=${m.value === decoded.misc}>
+              ${m.label}
+            </option>`)}
+        </select>
+      </label>`;
+  }
+
+  private _renderChainActionsSection(actions: ProgramFields[]): TemplateResult {
+    return html`
+      <fieldset>
+        <legend>
+          Actions (${actions.length})
+          <button type="button" class="mini-btn"
+            @click=${() => this._addChainAction()}>+ THEN</button>
+        </legend>
+        ${actions.map((a, idx) => this._renderChainActionRow(a, idx, actions.length))}
+      </fieldset>
+    `;
+  }
+
+  private _renderChainActionRow(
+    action: ProgramFields, idx: number, total: number,
+  ): TemplateResult {
+    const cmdOpt: CommandOption | undefined = commandOptionFor(action.cmd ?? 0);
+    const objectBucket = cmdOpt?.ref_kind
+      ? this._bucketWithPreserve(
+          this._pickBucket(cmdOpt.ref_kind),
+          cmdOpt.ref_kind,
+          action.pr2 ?? 0,
+        )
+      : null;
+    const showsLevelPercent = action.cmd === 9;
+    return html`
+      <div class="cond-slot">
+        <div class="cond-row-header">
+          <strong>${idx === 0 ? "THEN" : "AND"}</strong>
+          ${total > 1 ? html`
+            <button type="button" class="mini-btn danger"
+              @click=${() => this._removeChainAction(idx)}>×</button>` : ""}
+        </div>
+        <label class="block">
+          Command
+          <select @change=${(e: Event) => {
+            const value = parseInt((e.target as HTMLSelectElement).value, 10);
+            const opt = commandOptionFor(value);
+            let newPr2 = action.pr2 ?? 0;
+            if (opt?.ref_kind && this._objects) {
+              const bucket = this._pickBucket(opt.ref_kind);
+              if (bucket && bucket.length > 0 &&
+                  !bucket.some((o) => o.index === newPr2)) {
+                newPr2 = bucket[0].index;
+              }
+            } else if (!opt?.ref_kind) {
+              newPr2 = 0;
+            }
+            this._patchChainAction(idx, { cmd: value, pr2: newPr2 });
+          }}>
+            ${COMMAND_OPTIONS.map((c) => html`
+              <option .value=${String(c.value)} ?selected=${c.value === action.cmd}>
+                ${c.label}
+              </option>`)}
+          </select>
+        </label>
+        ${cmdOpt?.ref_kind ? html`
+          <label class="block">
+            ${cmdOpt.ref_kind[0].toUpperCase() + cmdOpt.ref_kind.slice(1)}
+            <select @change=${(e: Event) => {
+              const v = parseInt((e.target as HTMLSelectElement).value, 10);
+              if (Number.isFinite(v)) this._patchChainAction(idx, { pr2: v });
+            }}>
+              ${(objectBucket ?? []).map((o) => html`
+                <option .value=${String(o.index)} ?selected=${o.index === action.pr2}>
+                  #${o.index} ${o.name}
+                </option>`)}
+            </select>
+          </label>` : ""}
+        ${showsLevelPercent ? html`
+          <label class="block">
+            Level (0..100)
+            <input type="number" min="0" max="100"
+              .value=${String(action.par ?? 0)}
+              @input=${(e: Event) => {
+                const v = parseInt((e.target as HTMLInputElement).value, 10);
+                if (Number.isFinite(v) && v >= 0 && v <= 100) {
+                  this._patchChainAction(idx, { par: v });
+                }
+              }}
+            />
+          </label>` : ""}
+      </div>
+    `;
+  }
+
   // -- styles -----------------------------------------------------------
 
   static styles = css`
@@ -1724,6 +2437,37 @@ export class OmniPanelPrograms extends LitElement {
       font-weight: 600;
       color: var(--primary-text-color, #000);
     }
+    .cond-row-header {
+      display: flex; justify-content: space-between; align-items: center;
+      margin-bottom: 4px;
+    }
+    .mini-btn {
+      border: 1px solid var(--divider-color, #ccc);
+      background: var(--card-background-color, #fff);
+      color: inherit;
+      padding: 2px 8px;
+      border-radius: 3px;
+      font-size: 0.78rem;
+      cursor: pointer;
+      font-family: inherit;
+      margin-left: 6px;
+    }
+    .mini-btn:hover { background: var(--secondary-background-color, #eee); }
+    .mini-btn.danger {
+      color: var(--error-color, #db4437);
+      border-color: var(--error-color, #db4437);
+    }
+    .structured-cond {
+      background: rgba(255, 152, 0, 0.08);  /* subtle warning tint */
+    }
+    .chain-meta {
+      margin-top: 8px;
+      padding: 8px 10px;
+      font-size: 0.82rem;
+      color: var(--secondary-text-color, #666);
+      background: var(--secondary-background-color, #f5f5f5);
+      border-radius: 4px;
+    }
   `;
 }
 

custom_components/omni_pca/frontend/src/types.ts

@@ -50,6 +50,13 @@ export interface ProgramDetail {
   /** Raw Program field values; included for compact-form programs so
    *  the editor can seed its form from real data rather than defaults. */
   fields?: ProgramFields;
+  /** For chain detail: per-member role + raw fields. Drives the
+   *  chain editor's row-per-slot rendering. */
+  chain_members?: Array<{
+    slot: number;
+    role: "head" | "condition" | "action";
+    fields: ProgramFields;
+  }>;
 }
 
 export interface ProgramListRequest {
@@ -409,6 +416,137 @@ export function encodeCondition(c: DecodedCondition): number {
   }
 }
 
+
+// --------------------------------------------------------------------------
+// Clausal chain (multi-record) editor types
+// --------------------------------------------------------------------------
+
+
+/** ProgramType values for the chain head/body/tail records. */
+export const PROGRAM_TYPE_WHEN = 5;
+export const PROGRAM_TYPE_AT = 6;
+export const PROGRAM_TYPE_EVERY = 7;
+export const PROGRAM_TYPE_AND = 8;
+export const PROGRAM_TYPE_OR = 9;
+export const PROGRAM_TYPE_THEN = 10;
+
+/** Roles assigned by the backend's chain_members payload. */
+export type ChainMemberRole = "head" | "condition" | "action";
+
+export interface ChainMember {
+  slot: number;
+  role: ChainMemberRole;
+  fields: ProgramFields;
+}
+
+/** Decoded view of a Traditional AND/OR record's condition.
+ *
+ * AND records use the SAME family encoding as compact-form cond, but
+ * the bytes land in different ProgramFields slots:
+ *
+ *   family   = fields.cond & 0xFF              (disk byte 1)
+ *   instance = (fields.cond2 >> 8) & 0xFF      (disk byte 3)
+ *
+ * The selector bit (`0x0200`) doesn't apply to AND records the same
+ * way — instead the family byte's bit 1 (0x02) carries the
+ * secure/not-ready or off/on selector. For example:
+ *   0x04 = ZONE secure         0x06 = ZONE not-ready
+ *   0x08 = CTRL off            0x0A = CTRL on
+ *   0x0C = TIME disabled       0x0E = TIME enabled
+ */
+export function decodeAndCondition(fields: ProgramFields): DecodedCondition {
+  const family = (fields.cond ?? 0) & 0xFF;
+  const instance = ((fields.cond2 ?? 0) >> 8) & 0xFF;
+  const familyMajor = family & 0xFC;
+  const selector = (family & 0x02) !== 0;
+  if (family === 0 && instance === 0) return { family: "none" };
+  if (familyMajor === 0x00) return { family: "misc", misc: family & 0x0F };
+  if (familyMajor === 0x04) return { family: "zone", index: instance, active: selector };
+  if (familyMajor === 0x08) return { family: "unit", index: instance, active: selector };
+  if (familyMajor === 0x0C) return { family: "time", index: instance, active: selector };
+  // SEC: high nibble of family = mode, low nibble = area.
+  return {
+    family: "sec",
+    index: family & 0x0F,
+    mode: (family >> 4) & 0x07,
+  };
+}
+
+/** Re-encode a DecodedCondition into the cond/cond2 fields of an
+ *  AND/OR record. Returns a partial ProgramFields with cond + cond2
+ *  set; the caller should merge with the rest of the record (cmd/par/
+ *  etc. stay zero for Traditional AND records).
+ */
+export function encodeAndCondition(c: DecodedCondition): {
+  cond: number; cond2: number;
+} {
+  switch (c.family) {
+    case "none":
+      return { cond: 0, cond2: 0 };
+    case "misc":
+      return { cond: (c.misc ?? 0) & 0x0F, cond2: 0 };
+    case "zone": {
+      const family = 0x04 | (c.active ? 0x02 : 0);
+      return { cond: family, cond2: ((c.index ?? 0) & 0xFF) << 8 };
+    }
+    case "unit": {
+      const family = 0x08 | (c.active ? 0x02 : 0);
+      return { cond: family, cond2: ((c.index ?? 0) & 0xFF) << 8 };
+    }
+    case "time": {
+      const family = 0x0C | (c.active ? 0x02 : 0);
+      return { cond: family, cond2: ((c.index ?? 0) & 0xFF) << 8 };
+    }
+    case "sec": {
+      const area = (c.index ?? 1) & 0x0F;
+      const mode = (c.mode ?? 0) & 0x07;
+      const family = (mode << 4) | area;
+      return { cond: family, cond2: 0 };
+    }
+  }
+}
+
+/** True if the AND/OR record's op byte indicates a Structured-OP
+ *  comparison (TEMP > 70 etc.) rather than the Traditional bit-packed
+ *  condition. Structured records use entirely different field
+ *  semantics; the editor in this pass renders them read-only.
+ *
+ *  OP byte lives at fields.cond >> 8 (disk byte 2). 0 = Traditional;
+ *  1..9 = Structured (CondOP enum).
+ */
+export function isStructuredAnd(fields: ProgramFields): boolean {
+  return (((fields.cond ?? 0) >> 8) & 0xFF) !== 0;
+}
+
+/** Build a fresh empty AND record (Traditional, NEVER condition). */
+export function emptyAndRecord(): ProgramFields {
+  return {
+    prog_type: PROGRAM_TYPE_AND,
+    cond: 0x01,    // family OTHER (0x00) + misc NEVER (0x01)
+    cond2: 0, cmd: 0, par: 0, pr2: 0,
+    month: 0, day: 0, days: 0, hour: 0, minute: 0,
+  };
+}
+
+/** Build a fresh empty OR record. Same shape as AND with a different
+ *  prog_type — semantically starts a new group in the conditions list.
+ */
+export function emptyOrRecord(): ProgramFields {
+  return { ...emptyAndRecord(), prog_type: PROGRAM_TYPE_OR };
+}
+
+/** Build a fresh empty THEN action record (Turn OFF unit 1). */
+export function emptyThenRecord(firstUnit: number = 1): ProgramFields {
+  return {
+    prog_type: PROGRAM_TYPE_THEN,
+    cmd: 0,        // UNIT_OFF
+    par: 0,
+    pr2: firstUnit,
+    cond: 0, cond2: 0,
+    month: 0, day: 0, days: 0, hour: 0, minute: 0,
+  };
+}
+
 /** HA's hass object — minimal surface we use. */
 export interface Hass {
   connection: {

custom_components/omni_pca/websocket.py

@@ -368,6 +368,21 @@ async def _ws_get_program(
             "tokens": _tokens_to_json(tokens),
             "references": _extract_references(tokens),
             "chain_slots": [m.slot for m in members if m.slot is not None],
+            # Per-member raw fields + role so the editor can render
+            # an editable form for each line of the clausal chain.
+            # role is "head" / "condition" / "action".
+            "chain_members": [
+                {
+                    "slot": m.slot,
+                    "role": (
+                        "head" if m is containing_chain.head
+                        else "action" if m in containing_chain.actions
+                        else "condition"
+                    ),
+                    "fields": _program_to_fields(m),
+                }
+                for m in members if m.slot is not None
+            ],
         })
         return
 
@@ -425,6 +440,159 @@ _PROGRAM_FIELD_SCHEMA = vol.Schema(
 )
 
 
+@websocket_api.websocket_command(
+    {
+        vol.Required("type"): "omni_pca/programs/chain/write",
+        vol.Required("entry_id"): str,
+        vol.Required("head_slot"): vol.All(int, vol.Range(min=1, max=1500)),
+        vol.Required("head"): dict,        # WHEN / AT / EVERY program dict
+        vol.Required("conditions"): [dict],
+        vol.Required("actions"): [dict],
+    }
+)
+@websocket_api.async_response
+async def _ws_chain_write(
+    hass: HomeAssistant,
+    connection: websocket_api.ActiveConnection,
+    msg: dict[str, Any],
+) -> None:
+    """Rewrite a clausal chain into consecutive slots.
+
+    A clausal program spans one head (WHEN/AT/EVERY) + N condition
+    records (AND/OR) + M action records (THEN), each in its own slot.
+    Editing means rewriting the whole run.
+
+    Logic:
+      1. Find the *existing* chain that owns ``head_slot`` (so we know
+         which old slots to clear when the chain shrinks).
+      2. The new run spans slots [head_slot .. head_slot + new_len - 1].
+         If new_len > old_len, the additional slots must currently be
+         FREE — refuse otherwise so we never trample an adjacent
+         program.
+      3. Write each new record via ``download_program``. The new run's
+         records are emitted in slot order; THEN actions land last.
+      4. Clear any old chain slots beyond the new run's end (shrinking
+         case) so leftover continuation records don't get mis-associated
+         with the now-shorter chain.
+    """
+    coordinator = _coordinator_for_entry(hass, msg["entry_id"])
+    if coordinator is None:
+        connection.send_error(msg["id"], "not_found", "panel not configured")
+        return
+    try:
+        client = coordinator.client
+    except RuntimeError as err:
+        connection.send_error(msg["id"], "not_connected", str(err))
+        return
+
+    from omni_pca.programs import Program  # local — avoid cycle
+
+    # Validate every member dict against the per-record schema (used
+    # individually so each member can have its own defaults).
+    try:
+        head_fields = _PROGRAM_FIELD_SCHEMA(msg["head"])
+        condition_fields = [_PROGRAM_FIELD_SCHEMA(c) for c in msg["conditions"]]
+        action_fields = [_PROGRAM_FIELD_SCHEMA(a) for a in msg["actions"]]
+    except vol.Invalid as err:
+        connection.send_error(msg["id"], "invalid", f"bad chain member: {err}")
+        return
+
+    if not action_fields:
+        connection.send_error(
+            msg["id"], "invalid", "chain must have at least one THEN action",
+        )
+        return
+
+    head_slot = msg["head_slot"]
+    new_len = 1 + len(condition_fields) + len(action_fields)
+
+    # Find the existing chain (if any) so we know which old slots are
+    # currently part of this program. Without an existing chain we still
+    # allow writing — that's the "create chain at this empty slot" case.
+    from omni_pca.program_engine import build_chains
+
+    programs = coordinator.data.programs if coordinator.data else {}
+    existing = next(
+        (c for c in build_chains(tuple(programs.values()))
+         if c.head.slot == head_slot),
+        None,
+    )
+    existing_slots: set[int] = set()
+    if existing is not None:
+        for m in (existing.head, *existing.conditions, *existing.actions):
+            if m.slot is not None:
+                existing_slots.add(m.slot)
+
+    new_slot_range = range(head_slot, head_slot + new_len)
+    if new_slot_range.stop > 1501:
+        connection.send_error(
+            msg["id"], "invalid",
+            f"chain of {new_len} records starting at slot {head_slot} "
+            f"would extend past slot 1500",
+        )
+        return
+
+    # Anti-trample check for any expansion slots that aren't already
+    # part of this chain.
+    for s in new_slot_range:
+        if s in existing_slots:
+            continue
+        if s in programs and not programs[s].is_empty():
+            connection.send_error(
+                msg["id"], "invalid",
+                f"target slot {s} is occupied by another program "
+                f"(slot {s}); free it first",
+            )
+            return
+
+    # Build the typed records.
+    head = Program(slot=head_slot, **head_fields)
+    new_records: list[tuple[int, Program]] = [(head_slot, head)]
+    for i, cf in enumerate(condition_fields):
+        slot = head_slot + 1 + i
+        new_records.append((slot, Program(slot=slot, **cf)))
+    actions_base = head_slot + 1 + len(condition_fields)
+    for i, af in enumerate(action_fields):
+        slot = actions_base + i
+        new_records.append((slot, Program(slot=slot, **af)))
+
+    # Write them in order.
+    try:
+        for slot, prog in new_records:
+            await client.download_program(slot, prog)
+    except NotImplementedError as err:
+        connection.send_error(msg["id"], "not_supported", str(err))
+        return
+    except Exception as err:
+        connection.send_error(msg["id"], "write_failed", str(err))
+        return
+
+    # Clear any old chain slot that's not in the new range (shrinking
+    # case). Order matters: clears come *after* writes so a transient
+    # observer never sees a half-rewritten chain.
+    to_clear = existing_slots - set(new_slot_range)
+    for slot in sorted(to_clear):
+        try:
+            await client.clear_program(slot)
+        except Exception:
+            # Don't fail the whole write for a clear-failure; log and continue.
+            _log.warning("failed to clear shrunk-away slot %s", slot)
+
+    # Update coordinator state. Same shape as single-slot write: drop
+    # cleared slots, set written slots.
+    if coordinator.data is not None:
+        for slot, prog in new_records:
+            coordinator.data.programs[slot] = prog
+        for slot in to_clear:
+            coordinator.data.programs.pop(slot, None)
+
+    connection.send_result(msg["id"], {
+        "head_slot": head_slot,
+        "written_slots": list(new_slot_range),
+        "cleared_slots": sorted(to_clear),
+    })
+
+
 @websocket_api.websocket_command(
     {
         vol.Required("type"): "omni_pca/objects/list",
@@ -705,6 +873,7 @@ def async_register_websocket_commands(hass: HomeAssistant) -> None:
     websocket_api.async_register_command(hass, _ws_clear_program)
     websocket_api.async_register_command(hass, _ws_clone_program)
     websocket_api.async_register_command(hass, _ws_write_program)
+    websocket_api.async_register_command(hass, _ws_chain_write)
     websocket_api.async_register_command(hass, _ws_list_objects)
 
 

tests/ha_integration/test_program_websocket.py

@@ -45,6 +45,27 @@ def seeded_programs() -> dict[int, Program]:
             # WHEN zone 1 changes to NOT_READY (event_id = 0x0401)
             month=0x04, day=0x01,
         ),
+        # A clausal chain spanning slots 200..203: WHEN zone 1 not-ready
+        # AND IF unit 1 ON THEN turn ON unit 2 AND turn OFF unit 1.
+        200: Program(
+            slot=200, prog_type=int(ProgramType.WHEN),
+            # event_id = 0x0401 (zone 1 not-ready) packed in month/day
+            month=0x04, day=0x01,
+        ),
+        201: Program(
+            slot=201, prog_type=int(ProgramType.AND),
+            # Traditional AND: family byte 0x0A = CTRL+ON, instance 1.
+            # and_family = cond & 0xFF, and_instance = (cond2>>8) & 0xFF.
+            cond=0x000A, cond2=0x0100,
+        ),
+        202: Program(
+            slot=202, prog_type=int(ProgramType.THEN),
+            cmd=int(Command.UNIT_ON), pr2=2,
+        ),
+        203: Program(
+            slot=203, prog_type=int(ProgramType.THEN),
+            cmd=int(Command.UNIT_OFF), pr2=1,
+        ),
     }
 
 
@@ -93,17 +114,14 @@ async def test_ws_list_programs_returns_summaries(
     response = await client.receive_json()
     assert response["success"] is True
     result = response["result"]
-    assert result["total"] == 3
-    assert result["filtered_total"] == 3
+    # 3 compact-form programs (12, 42, 99) + 1 clausal chain (head at
+    # slot 200, spanning 200..203). The chain renders as a single row.
+    assert result["total"] == 4
+    assert result["filtered_total"] == 4
     rows_by_slot = {row["slot"]: row for row in result["programs"]}
-    # Both TIMED programs and the EVENT program land in the response.
-    assert rows_by_slot.keys() == {12, 42, 99}
-    # Each row has the metadata the frontend needs.
-    for row in result["programs"]:
-        assert row["kind"] == "compact"
-        assert row["trigger_type"] in ("TIMED", "EVENT")
-        assert isinstance(row["summary"], list)
-        assert row["summary"]  # non-empty token list
+    assert rows_by_slot.keys() == {12, 42, 99, 200}
+    assert rows_by_slot[200]["kind"] == "chain"
+    assert rows_by_slot[12]["kind"] == "compact"
 
 
 async def test_ws_list_programs_filter_by_trigger_type(
@@ -135,8 +153,11 @@ async def test_ws_list_programs_filter_by_referenced_entity(
     })
     response = await client.receive_json()
     result = response["result"]
-    assert result["filtered_total"] == 1
-    assert result["programs"][0]["slot"] == 42
+    # Slot 42 ("Turn ON KITCHEN_OVERHEAD" = unit 2) plus the seeded chain
+    # at slot 200 (action: Turn ON unit 2) both reference unit:2.
+    assert result["filtered_total"] == 2
+    slots = {r["slot"] for r in result["programs"]}
+    assert slots == {42, 200}
 
 
 async def test_ws_list_programs_search_substring(
@@ -151,9 +172,13 @@ async def test_ws_list_programs_search_substring(
     })
     response = await client.receive_json()
     result = response["result"]
-    # Only slot 42 ("Turn ON KITCHEN_OVERHEAD") mentions kitchen.
-    assert result["filtered_total"] == 1
-    assert result["programs"][0]["slot"] == 42
+    # Slot 42 ("Turn ON KITCHEN_OVERHEAD" — truncated to 12 chars on
+    # wire = "KITCHEN_OVER") matches. The chain at slot 200 also has
+    # an action against unit 2 which renders with the same truncated
+    # name, so it matches too.
+    assert result["filtered_total"] == 2
+    slots = {r["slot"] for r in result["programs"]}
+    assert slots == {42, 200}
 
 
 async def test_ws_list_programs_pagination(
@@ -168,7 +193,8 @@ async def test_ws_list_programs_pagination(
     })
     response = await client.receive_json()
     result = response["result"]
-    assert result["filtered_total"] == 3
+    # 4 list rows total: 3 compact + 1 chain head.
+    assert result["filtered_total"] == 4
     assert len(result["programs"]) == 2
     assert [row["slot"] for row in result["programs"]] == [42, 99]
 
@@ -462,6 +488,167 @@ async def test_ws_list_objects_returns_named_buckets(
     assert zones_by_idx[1] == "FRONT_DOOR"
 
 
+async def test_ws_get_chain_returns_member_fields(
+    hass: HomeAssistant, configured_panel, hass_ws_client
+) -> None:
+    """Chain detail response includes a chain_members array with each
+    member's role + raw fields, so the editor can render an editable
+    row per slot."""
+    client = await hass_ws_client(hass)
+    await client.send_json_auto_id({
+        "type": "omni_pca/programs/get",
+        "entry_id": configured_panel.entry_id,
+        "slot": 200,  # head of the seeded chain
+    })
+    response = await client.receive_json()
+    assert response["success"] is True
+    result = response["result"]
+    assert result["kind"] == "chain"
+    members = result["chain_members"]
+    roles = [m["role"] for m in members]
+    assert roles == ["head", "condition", "action", "action"]
+    # Head carries the event_id (zone 1 NOT_READY = 0x0401).
+    head_fields = members[0]["fields"]
+    assert head_fields["prog_type"] == int(ProgramType.WHEN)
+    assert head_fields["month"] == 0x04
+    assert head_fields["day"] == 0x01
+    # Condition is a Traditional AND record with family CTRL+ON, unit 1.
+    cond_fields = members[1]["fields"]
+    assert cond_fields["prog_type"] == int(ProgramType.AND)
+    assert cond_fields["cond"] == 0x000A
+    assert cond_fields["cond2"] == 0x0100
+
+
+async def test_ws_chain_write_replaces_in_place(
+    hass: HomeAssistant, configured_panel, hass_ws_client
+) -> None:
+    """Same-length rewrite leaves the chain footprint unchanged but
+    updates every member's bytes."""
+    client = await hass_ws_client(hass)
+    coordinator = hass.data[DOMAIN][configured_panel.entry_id]
+    # Existing chain: slots 200..203.
+    assert {200, 201, 202, 203} <= coordinator.data.programs.keys()
+    await client.send_json_auto_id({
+        "type": "omni_pca/programs/chain/write",
+        "entry_id": configured_panel.entry_id,
+        "head_slot": 200,
+        "head": {
+            "prog_type": int(ProgramType.WHEN),
+            "month": 0x04, "day": 0x02,        # zone 1 trouble (id 0x0402)
+        },
+        "conditions": [
+            # AND IF unit 2 ON (family 0x0A, instance 2)
+            {"prog_type": int(ProgramType.AND),
+             "cond": 0x000A, "cond2": 0x0200},
+        ],
+        "actions": [
+            {"prog_type": int(ProgramType.THEN),
+             "cmd": int(Command.UNIT_OFF), "pr2": 2},
+            {"prog_type": int(ProgramType.THEN),
+             "cmd": int(Command.UNIT_ON), "pr2": 1},
+        ],
+    })
+    response = await client.receive_json()
+    assert response["success"] is True
+    assert response["result"]["written_slots"] == [200, 201, 202, 203]
+    assert response["result"]["cleared_slots"] == []
+    # Coordinator state reflects the new bytes.
+    assert coordinator.data.programs[200].day == 0x02
+    assert coordinator.data.programs[201].cond2 == 0x0200
+    assert coordinator.data.programs[202].cmd == int(Command.UNIT_OFF)
+
+
+async def test_ws_chain_write_shrinks_and_clears(
+    hass: HomeAssistant, configured_panel, hass_ws_client
+) -> None:
+    """Shorter rewrite clears the trailing old chain slots."""
+    client = await hass_ws_client(hass)
+    coordinator = hass.data[DOMAIN][configured_panel.entry_id]
+    await client.send_json_auto_id({
+        "type": "omni_pca/programs/chain/write",
+        "entry_id": configured_panel.entry_id,
+        "head_slot": 200,
+        "head": {
+            "prog_type": int(ProgramType.WHEN),
+            "month": 0x04, "day": 0x01,
+        },
+        # No conditions, one action — chain shrinks from 4 slots to 2.
+        "conditions": [],
+        "actions": [
+            {"prog_type": int(ProgramType.THEN),
+             "cmd": int(Command.UNIT_ON), "pr2": 1},
+        ],
+    })
+    response = await client.receive_json()
+    assert response["success"] is True
+    assert response["result"]["written_slots"] == [200, 201]
+    assert sorted(response["result"]["cleared_slots"]) == [202, 203]
+    # Cleared slots are gone from the coordinator's view.
+    assert 202 not in coordinator.data.programs
+    assert 203 not in coordinator.data.programs
+
+
+async def test_ws_chain_write_refuses_to_trample(
+    hass: HomeAssistant, configured_panel, hass_ws_client
+) -> None:
+    """Expanding a chain into a slot that already holds another program
+    is refused — protects against accidental data loss."""
+    client = await hass_ws_client(hass)
+    coordinator = hass.data[DOMAIN][configured_panel.entry_id]
+    # Seed a sentinel program at slot 204 (right after the chain) so an
+    # expand attempt collides.
+    coordinator.data.programs[204] = Program(
+        slot=204, prog_type=int(ProgramType.TIMED),
+        cmd=int(Command.UNIT_ON), pr2=1,
+        hour=12, minute=0, days=int(Days.MONDAY),
+    )
+    await client.send_json_auto_id({
+        "type": "omni_pca/programs/chain/write",
+        "entry_id": configured_panel.entry_id,
+        "head_slot": 200,
+        "head": {"prog_type": int(ProgramType.WHEN),
+                 "month": 0x04, "day": 0x01},
+        "conditions": [
+            {"prog_type": int(ProgramType.AND),
+             "cond": 0x000A, "cond2": 0x0100},
+            # Adding a second condition pushes the chain from 4 to 5
+            # slots → slot 204 collision.
+            {"prog_type": int(ProgramType.AND),
+             "cond": 0x000A, "cond2": 0x0200},
+        ],
+        "actions": [
+            {"prog_type": int(ProgramType.THEN),
+             "cmd": int(Command.UNIT_ON), "pr2": 2},
+            {"prog_type": int(ProgramType.THEN),
+             "cmd": int(Command.UNIT_OFF), "pr2": 1},
+        ],
+    })
+    response = await client.receive_json()
+    assert response["success"] is False
+    assert response["error"]["code"] == "invalid"
+    # The sentinel program is untouched.
+    assert coordinator.data.programs[204].cmd == int(Command.UNIT_ON)
+
+
+async def test_ws_chain_write_rejects_zero_actions(
+    hass: HomeAssistant, configured_panel, hass_ws_client
+) -> None:
+    """A chain with no THEN actions is meaningless — refuse it."""
+    client = await hass_ws_client(hass)
+    await client.send_json_auto_id({
+        "type": "omni_pca/programs/chain/write",
+        "entry_id": configured_panel.entry_id,
+        "head_slot": 200,
+        "head": {"prog_type": int(ProgramType.WHEN),
+                 "month": 0x04, "day": 0x01},
+        "conditions": [],
+        "actions": [],
+    })
+    response = await client.receive_json()
+    assert response["success"] is False
+    assert response["error"]["code"] == "invalid"
+
+
 async def test_ws_list_programs_live_state_overlay_zone(
     hass: HomeAssistant, configured_panel, hass_ws_client
 ) -> None: