Add prev/next textbook nav to wiki pages (#77)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

tools/build_wiki.py

@@ -8,7 +8,8 @@ the `--host` URL flavor and the CI wrapper differ.
 
 The wiki is GENERATED BUILD OUTPUT. Never hand-edit it; edit modules/ and let CI
 re-render. Labs are NOT copied into the wiki — lesson pages link to the runnable
-files back in the main repo.
+files back in the main repo. Each page gets prev/next navigation so the wiki reads
+like a textbook.
 
 Usage:
   build_wiki.py --repo-root . --out <wiki-dir> \
@@ -105,6 +106,19 @@ def home_intro(repo_root: Path) -> str:
     return "\n".join(out).strip()
 
 
+def top_nav(prev) -> str:
+    """prev is (page, label) or None."""
+    if not prev:
+        return ""
+    return f"⬅ **Previous: [{prev[1]}]({prev[0]})**\n"
+
+
+def bottom_nav(nxt) -> str:
+    if not nxt:
+        return ""
+    return f"**Continue to: [{nxt[1]}]({nxt[0]})** ➡\n"
+
+
 def main() -> int:
     ap = argparse.ArgumentParser()
     ap.add_argument("--repo-root", default=".")
@@ -123,43 +137,47 @@ def main() -> int:
         print("no modules found", flush=True)
         return 1
 
+    # --- pass 1: read everything, build the ordered reading sequence ------
+    # each entry: {page, label, body, slug|None}
+    seq = []
     titles: dict[int, str] = {}
     slugs: dict[int, str] = {}
-
-    # --- per-module pages -------------------------------------------------
     for num, slug, path in mods:
         body = (path / "README.md").read_text(encoding="utf-8")
         h1 = first_h1(body, f"Module {num}")
         titles[num] = h1
         slugs[num] = slug
-        source_path = f"modules/{slug}/README.md"
-        body = rewrite_lab_links(body, args.web_base, args.branch, args.host, slug)
-        body = rewrite_repo_file_links(body, args.web_base, args.branch, args.host)
-        page = (
-            banner(source_path, src_url(args.web_base, args.branch, args.host, source_path))
-            + "\n"
-            + body
-            + "\n"
-        )
-        (out / f"{slug}.md").write_text(page, encoding="utf-8")
+        seq.append({"page": slug, "label": h1, "body": body, "slug": slug})
 
-    # --- capstone ---------------------------------------------------------
     cap = repo_root / "capstone" / "README.md"
     cap_title = None
     if cap.exists():
         body = cap.read_text(encoding="utf-8")
         cap_title = first_h1(body, "Capstone — The Full Loop")
-        source_path = "capstone/README.md"
-        # capstone labs may reference modules/.. ; only lab/ links are rewritten elsewhere,
-        # capstone has none, so copy through with a banner.
-        body = rewrite_repo_file_links(body, args.web_base, args.branch, args.host)
-        page = (
-            banner(source_path, src_url(args.web_base, args.branch, args.host, source_path))
-            + "\n"
-            + body
-            + "\n"
-        )
-        (out / "capstone.md").write_text(page, encoding="utf-8")
+        seq.append({"page": "capstone", "label": cap_title, "body": body, "slug": None})
+
+    # --- pass 2: write each page with banner + prev/next nav --------------
+    for i, entry in enumerate(seq):
+        prev = (seq[i - 1]["page"], seq[i - 1]["label"]) if i > 0 else None
+        nxt = (seq[i + 1]["page"], seq[i + 1]["label"]) if i < len(seq) - 1 else None
+
+        if entry["slug"] is not None:
+            source_path = f"modules/{entry['slug']}/README.md"
+            body = rewrite_lab_links(entry["body"], args.web_base, args.branch, args.host, entry["slug"])
+            body = rewrite_repo_file_links(body, args.web_base, args.branch, args.host)
+        else:
+            source_path = "capstone/README.md"
+            body = rewrite_repo_file_links(entry["body"], args.web_base, args.branch, args.host)
+
+        parts = [banner(source_path, src_url(args.web_base, args.branch, args.host, source_path))]
+        tn = top_nav(prev)
+        if tn:
+            parts.append("\n" + tn)
+        parts.append("\n" + body)
+        bn = bottom_nav(nxt)
+        if bn:
+            parts.append("\n---\n\n" + bn)
+        (out / f"{entry['page']}.md").write_text("\n".join(parts) + "\n", encoding="utf-8")
 
     # --- _Sidebar.md (textbook nav) --------------------------------------
     sb = ["### [📖 Home](Home)\n"]
@@ -205,9 +223,10 @@ def main() -> int:
         encoding="utf-8",
     )
 
-    pages = len(mods) + (1 if cap_title else 0) + 3
+    pages = len(seq) + 3
     print(f"wrote {pages} wiki files to {out} ({len(mods)} modules"
-          f"{' + capstone' if cap_title else ''} + Home/_Sidebar/_Footer)", flush=True)
+          f"{' + capstone' if cap_title else ''} + Home/_Sidebar/_Footer, with prev/next nav)",
+          flush=True)
     return 0