docs: include Journal execution guide in Dune odoc output

app/spec/README.md

@@ -4,6 +4,11 @@
   walkthrough of the important App, Worker and Sync paths using existing spec
   types and pseudocode. It exports no interface and adds no virtual library.
 
+Run `dune build @doc` and open `_build/default/_doc/_html/logseq_journal/index.html`.
+The package homepage links to the execution guide and the coordination API.
+The guide's `.mld` page is generated from its single `.mli` documentation comment;
+edit only the `.mli` body.
+
 Each area under this directory is an independent wrapped Dune virtual library.
 Do not use recursive `include_subdirs` to merge future specifications into one
 library. Add another area only when it has actual contracts and consumers.

app/spec/dune

@@ -0,0 +1,15 @@
+; Keep the documentation-only .mli as the sole body source.
+; Extract its single comment without adding an OCaml module or library.
+
+(rule
+ (target journal_execution_flow.mld)
+ (action
+  (with-stdout-to
+   %{target}
+   (progn
+    (echo "{0 Journal execution flow}\n\n")
+    (run sed -e "1s/^(\\*\\* *//" -e "$d" %{dep:journal_execution_flow.mli})))))
+
+(documentation
+ (package logseq_journal)
+ (mld_files index journal_execution_flow))

app/spec/index.mld

@@ -0,0 +1,10 @@
+{0 Logseq Journal}
+
+{1 Execution guide}
+
+{{!page-journal_execution_flow}Journal execution flow}: follow startup, reads,
+durable writes, synchronization and resource retirement through the existing specs.
+
+{1 Library logseq_journal.worker_coordination}
+
+The App/Worker coordination API is {!module-Journal_worker_coordination}.