feat(post-form): U1 — shared create/edit form + published field + owner_username

One /post form now drives both create and edit (KTD1, Alt B): cache-on-save
toggles add-page-by-form's overwrite_mode per submit — 'edit' when the new hidden
edit_path field is filled (write back in place, stable URL), 'false' when empty
(fresh dated folder via slug_field). add-page-by-form stays stock (no fork);
the toggle lives in cache-on-save, which reads edit_path and mutates the /post
page header's pageconfig before add-page-by-form's onFormProcessed runs.

- post-form.md: overwrite_mode:false (create-safe fallback), hidden edit_path,
  authoritative published toggle (default on), removed the static
  pagefrontmatter.published so the field wins on every submit (KTD3).
- cache-on-save.php: editPathFromForm + setOverwriteMode helpers.
- site.yaml: owner_username (single source of truth for the KTD8 owner gate).

Verified against the 2.0.4 container: create writes a fresh dated folder with
published:true/false as a real boolean (V1, V2); edit writes in place with the
slug/URL unchanged; save-as-draft-on-create works.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H1FrCYNq6RXdGYbn5PFrhM

config/site.yaml

@@ -7,3 +7,8 @@ metadata:
 description: 'A travel blog by Mischa'
 active_trip: /trips/us-canada-mex-2024
 travelling: false
+# Single source of truth for the site owner's account username. Backs both the
+# front-end edit/delete UI gate and the server-side scope guards (KTD8): only
+# this user (not merely any authenticated/super-admin account) may edit, delete,
+# or see drafts on the active trip's feed.
+owner_username: mischa

pages/02.post/post-form.md

@@ -6,13 +6,21 @@ access:
 
 # Parent (write target) is injected server-side from site.active_trip by the
 # cache-on-save plugin (onFormValidationProcessed) — no manual sync needed.
+#
+# overwrite_mode is toggled per submit by cache-on-save (KTD1, Alt B): edit when
+# the hidden edit_path field is filled (write back in place), false when empty
+# (create a fresh dated folder via slug_field). The static value here is the
+# create-safe fallback for if cache-on-save doesn't run — add-page-by-form stays
+# stock (no fork), so a static `edit` would break create (empty edit_path -> '.').
 pageconfig:
     slug_field: 'date,title'
     overwrite_mode: false
 
+# published is NOT a static pagefrontmatter default anymore — it is an
+# authoritative form field (below) so every submit (create AND edit) writes the
+# owner's chosen publish state. Only `template` stays static here.
 pagefrontmatter:
     template: entry
-    published: true
 
 form:
     name: new-entry
@@ -129,11 +137,36 @@ form:
                 'car': '🚗 Car'
                 'plane': '✈️ Plane'
 
+        # Hidden edit target. Empty on create (add-page-by-form falls through to
+        # slug_field and writes a fresh dated folder); on edit, post-form.js sets
+        # it to the entry's path so overwrite_mode:edit writes back in place.
+        -
+            name: edit_path
+            type: hidden
+            default: ''
+
         # Advanced fields — collapsed behind "More options" (see U5).
         # No hero_image field: journal entries render their hero from the first
         # uploaded photo (entry-journal.html.twig uses entry.media.images|first),
         # so an explicit hero filename was redundant. Stories still use hero_image
         # but they aren't posted through this form.
+        -
+            name: published
+            label: Published
+            # Authoritative publish state (replaces the removed static
+            # pagefrontmatter.published). Default ON so new entries publish; the
+            # owner flips it OFF to save/keep a draft, or to unpublish on edit.
+            # validate.type:bool keeps it a real boolean in frontmatter (not '0').
+            type: toggle
+            classes: advanced-field
+            highlight: 1
+            default: 1
+            options:
+                1: 'Yes'
+                0: 'No'
+            validate:
+                type: bool
+
         -
             name: force_connect
             label: Force connector line

plugins/cache-on-save/cache-on-save.php

@@ -48,6 +48,46 @@ class CacheOnSavePlugin extends Plugin
         }
 
         $form->setData('parent', $this->resolveDailiesParent($activeTrip));
+
+        // One shared /post form drives both create and edit (KTD1). add-page-by-form
+        // reads overwrite_mode from the /post page header's pageconfig (not form
+        // data), so we toggle it here per submit:
+        //  - edit  (edit_path present) -> overwrite_mode:edit, writes back in place
+        //  - create (edit_path empty)  -> overwrite_mode:false, so stock falls
+        //    through to slug_field (date,title) and writes a fresh dated folder.
+        // This keeps add-page-by-form stock (no fork), since a static
+        // overwrite_mode:edit would break create (empty edit_path slugs to '.').
+        $editPath = $this->editPathFromForm($form);
+        $this->setOverwriteMode($editPath === '' ? 'false' : 'edit');
+    }
+
+    /**
+     * The hidden edit_path form field, trimmed. Empty string when creating a new
+     * entry; the entry's `<route>/entry.md` path when editing (set by post-form.js).
+     */
+    private function editPathFromForm($form): string
+    {
+        $value = $form->value('edit_path');
+        return is_string($value) ? trim($value) : '';
+    }
+
+    /**
+     * Override add-page-by-form's overwrite_mode by mutating the current (/post)
+     * page header's pageconfig. add-page-by-form reads
+     * `$grav['page']->header()->pageconfig['overwrite_mode']` (add-page-by-form.php
+     * :385) from the same page singleton, and Page::header() returns a cached
+     * instance, so this write is visible when its onFormProcessed runs afterwards.
+     */
+    private function setOverwriteMode(string $mode): void
+    {
+        $page = $this->grav['page'] ?? null;
+        if (!$page) {
+            return;
+        }
+        $header = $page->header();
+        $pageconfig = (isset($header->pageconfig) && is_array($header->pageconfig)) ? $header->pageconfig : [];
+        $pageconfig['overwrite_mode'] = $mode;
+        $header->pageconfig = $pageconfig;
     }
 
     /**