docs: fix ARCHITECTURE.md mermaid diagrams + document the autosave last-mile guard

Rewrite all five mermaid blocks to portable syntax so they render (verified via
a mermaid-native render): split two `classDef`/`class` statements that shared a
line (the "why not just signals" graph); drop the `reduce() — PURE` participant
alias and the `;` inside a Note (§2c sequence); remove `<br/>` and parenthetical
transition labels from the two stateDiagram-v2 blocks (RemoteData, intake),
moving the aside into a note; normalize `<br/>`→`<br>` and drop `<b>` in the
atomic-hierarchy flowchart.

Extend §2g to document the now-closed gap: a CanDeactivate guard flushes the
pending debounce before in-app navigation, and beforeunload warns + best-effort
flushes on hard close (noting the HttpClient/keepalive limitation).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/reference/architecture/ARCHITECTURE.md

@@ -43,11 +43,11 @@ ever uses the level(s) below it — so anything you build is reusable by everyth
 
 ```mermaid
 graph TD
-    P["<b>Pages</b><br/>dashboard.page · login.page · intake.page"]
+    P["Pages<br>dashboard.page · login.page · intake.page"]
-    T["<b>Templates</b><br/>page-shell · shell"]
+    T["Templates<br>page-shell · shell"]
-    O["<b>Organisms</b><br/>login-form · registration-table · intake-wizard"]
+    O["Organisms<br>login-form · registration-table · intake-wizard"]
-    M["<b>Molecules</b><br/>form-field · data-row · async"]
+    M["Molecules<br>form-field · data-row · async"]
-    A["<b>Atoms</b><br/>button · text-input · radio-group · alert · heading"]
+    A["Atoms<br>button · text-input · radio-group · alert · heading"]
     P --> T --> O --> M --> A
     classDef l fill:#e5f1fb,stroke:#007bc7,color:#00567d;
     class P,T,O,M,A l;
@@ -110,12 +110,12 @@ the 4 states that are real** — the illegal ones can't be expressed at all.
 graph LR
     subgraph bad["3 booleans = 8 states (most illegal)"]
         direction TB
-        b1["loading ✓ · error ✗ · data ✗  ✅"]
+        b1["loading ✓ · error ✗ · data ✗ — legal"]
-        b2["loading ✗ · error ✓ · data ✗  ✅"]
+        b2["loading ✗ · error ✓ · data ✗ — legal"]
-        b3["loading ✗ · error ✗ · data ✓  ✅"]
+        b3["loading ✗ · error ✗ · data ✓ — legal"]
-        b4["loading ✓ · error ✓ · data ✓  ❌ nonsense"]
+        b4["loading ✓ · error ✓ · data ✓ — nonsense"]
-        b5["loading ✓ · error ✗ · data ✓  ❌ nonsense"]
+        b5["loading ✓ · error ✗ · data ✓ — nonsense"]
-        b6["… 3 more illegal combos ❌"]
+        b6["… 3 more illegal combos"]
     end
     subgraph good["1 union = 4 legal states"]
         direction TB
@@ -125,8 +125,10 @@ graph LR
         g4["Success (carries value)"]
     end
     bad -->|"choose a better type"| good
-    classDef ok fill:#e8f5e9,stroke:#39870c; classDef no fill:#fdecea,stroke:#d52b1e;
+    classDef ok fill:#e8f5e9,stroke:#39870c;
-    class b1,b2,b3,g1,g2,g3,g4 ok; class b4,b5,b6 no;
+    classDef no fill:#fdecea,stroke:#d52b1e;
+    class b1,b2,b3,g1,g2,g3,g4 ok;
+    class b4,b5,b6 no;
 ```
 
 The same argument applies to forms (a `submitting` boolean that can be true _with_
@@ -175,7 +177,7 @@ stateDiagram-v2
     Loading --> Success: data arrived
     Loading --> Empty: arrived, but no rows
     Loading --> Failure: request failed
-    Failure --> Loading: reload()
+    Failure --> Loading: reload
     note right of Success
         value lives ONLY here
     end note
@@ -230,15 +232,15 @@ _one_ function. No state is mutated anywhere else.
 ```mermaid
 sequenceDiagram
     actor User
-    participant View as View (template)
+    participant View
-    participant Store as createStore (signal)
+    participant Store
-    participant Reduce as reduce() — PURE
+    participant Reduce
     User->>View: clicks / types
     View->>Store: dispatch(msg)
-    Store->>Reduce: reduce(model, msg)
+    Store->>Reduce: reduce(model, msg) — PURE
     Reduce-->>Store: next model
-    Store-->>View: signal updates → re-render
+    Store-->>View: signal updates, re-render
-    Note over Reduce: the ONLY place state changes;<br/>no HTTP, no timers, no mutation
+    Note over Reduce: the ONLY place state changes<br>no HTTP, no timers, no mutation
 ```
 
 Side effects (HTTP) sit _outside_ this loop: a command does the I/O, then `dispatch`es a
@@ -366,6 +368,22 @@ So it _feels_ like save-on-blur only because you usually stop typing when you le
 field, and the debounce fires ~600 ms later. The trigger is **"stopped changing," not
 "lost focus."** Submit is a separate, explicit action (§2d).
 
+**The last-mile guard (leaving mid-debounce).** A debounce means an edit made in the final
+&lt;600 ms before you leave hasn't been written yet. Two seams close that window
+([`pending-saves.ts`](../../../src/app/shared/application/pending-saves.ts)): every autosave
+owner (the brief/org-template root stores and each wizard's `draft-sync`) registers in a
+`PendingSaves` registry, and
+
+- **in-app navigation** — a `CanDeactivate` guard (`flushPendingGuard`, on the autosave
+  routes) flushes the pending write and _awaits_ it before the route changes, so the page
+  can't tear down with an unsaved keystroke;
+- **hard close / reload** — a `beforeunload` handler fires the flush best-effort and triggers
+  the browser's native "unsaved changes" prompt. It is deliberately _not_ a guaranteed sync
+  save: the HTTP seam is Angular `HttpClient` (no `keepalive`/`sendBeacon`), so an async write
+  can't be promised to finish as the page unloads — the prompt lets the debounce land if the
+  user stays. The authoritative _submit_ path already force-flushes first, so only unsent
+  draft keystrokes are ever at risk.
+
 ---
 
 ## 3. "Parse, don't validate" — value objects
@@ -443,11 +461,14 @@ where the user left off.
 ```mermaid
 stateDiagram-v2
     [*] --> Answering
-    Answering --> Answering: SetAnswer / Next / Back<br/>(steps re-derived each time)
+    Answering --> Answering: SetAnswer / Next / Back
-    Answering --> Submitting: Submit (all answers valid)
+    Answering --> Submitting: Submit when all answers valid
     Submitting --> Submitted: ok
     Submitting --> Failed: error
     Failed --> Submitting: Retry
+    note right of Answering
+        steps re-derived each time
+    end note
 ```
 
 See it live on `/concepts` (section 5) — the step list and the "stap N van M" counter