docs: add AGENTS.md with workflow conventions

AGENTS.md

@@ -0,0 +1,28 @@
+# Spine — Agent Workflow
+
+## Branch Strategy
+
+This project does not use pull requests or feature branches. All work is committed
+directly to `main` and pushed.
+
+## Workflow
+
+1. **Commit early, commit often** — small, focused commits with clear messages.
+2. **Push after each logical batch** — don't accumulate un-pushed work.
+3. **Test before push** — run the relevant test suite; don't push known failures.
+
+## Commit Messages
+
+Use conventional commits:
+- `feat:` for new features
+- `fix:` for bug fixes
+- `test:` for test additions/changes
+- `docs:` for documentation
+- `refactor:` for code restructuring
+
+## Verification
+
+Run tests before pushing:
+```bash
+emacs --batch -l test/<test-file>.el --eval "(ert-run-tests-batch-and-exit)"
+```

docs/plans/2026-06-21-concise-default-view.md

@@ -0,0 +1,478 @@
+# Concise Default View Implementation Plan
+
+**Goal:** Default index shows only READING + 5 most recent WANT books, with filter links to expanded views.
+
+**Architecture:** `spine-index-model` gains an optional `filter` argument (nil = concise, "all"/"read"/"want" = expanded). The handler reads `filter` from the request query and passes it through. The template gains conditional nav links and summary-group rows. Existing group rendering unchanged.
+
+**Tech Stack:** Emacs Lisp (model/handler), Mustache (template)
+
+---
+
+## File overview
+
+**Modify:**
+- `spine.el` — `spine-index-model` (add filter param, concise logic), `defservlet index` (pass query filter)
+- `templates/index.mustache` — filter nav bar, summary-group rows
+- `test/spine-index-model-test.el` — new test file for filtered model
+
+---
+
+### Task 1: Write failing tests for filtered `spine-index-model`
+
+**Files:**
+- Create: `test/spine-index-model-test.el`
+
+- [ ] **Step 1: Create test file with setup**
+
+```elisp
+;;; spine-index-model-test.el — ERT tests for spine-index-model with filter
+
+(require 'ert)
+(require 'cl-lib)
+
+(setq spine-skip-server-start t)
+(setq spine-org-file (expand-file-name "sample-books.org"
+                                       (file-name-directory
+                                        (directory-file-name
+                                         (file-name-directory load-file-name)))))
+(load-file (expand-file-name "../spine.el"
+                             (file-name-directory load-file-name)))
+
+(defconst spine-index-model-test--books (spine-books)
+  "Books fixture loaded once from sample-books.org.")
+```
+
+- [ ] **Step 2: Write test — concise view excludes READ and ABANDONED groups, has summary**
+
+```elisp
+(ert-deftest spine-index-model-concise-hides-read-and-abandoned ()
+  "Concise view (filter=nil) omits READ/ABANDONED groups, adds summary-groups."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should-not (member "read" group-labels))
+    (should-not (member "abandoned" group-labels))
+    (should summaries)
+    (should (= (length summaries) 1))   ; only READ, no ABANDONED in sample data
+    (should (string= (ht-get (car summaries) "label") "read"))
+    (should (= (ht-get (car summaries) "count") 1))  ; Ancillary Justice
+    (should (string= (ht-get (car summaries) "href") "/index?filter=read"))))
+```
+
+- [ ] **Step 3: Write test — concise view includes READING group**
+
+```elisp
+(ert-deftest spine-index-model-concise-includes-reading ()
+  "Concise view includes READING group with all reading books."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (reading-group (cl-find "reading" groups
+                                 :key (lambda (g) (ht-get g "label"))
+                                 :test #'string=)))
+    (should reading-group)
+    (should (= (ht-get reading-group "count") 1))   ; Use of Weapons
+    (should (string= (ht-get (car (ht-get reading-group "books")) "title")
+                     "Use of Weapons"))))
+```
+
+- [ ] **Step 4: Write test — concise view limits WANT to 5 most recent**
+
+```elisp
+(ert-deftest spine-index-model-concise-want-limited-to-five ()
+  "Concise view limits WANT group to 5 books, sorted by :ADDED: desc."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (want-group (cl-find "on deck" groups
+                              :key (lambda (g) (ht-get g "label"))
+                              :test #'string=)))
+    (should want-group)
+    (let ((books (ht-get want-group "books")))
+      (should (<= (length books) 5))
+      ;; sample-books.org has 3 WANT books — all should appear, sorted newest first
+      (should (= (length books) 3))
+      ;; Piranesi added 2026-06-01, Dune 2026-05-10, Left Hand 2026-04-01
+      (should (string= (ht-get (nth 0 books) "title") "Piranesi"))
+      (should (string= (ht-get (nth 1 books) "title") "Dune"))
+      (should (string= (ht-get (nth 2 books) "title") "The Left Hand of Darkness")))))
+```
+
+- [ ] **Step 5: Write test — filter=all returns full model (no summary, all groups)**
+
+```elisp
+(ert-deftest spine-index-model-filter-all-shows-all-groups ()
+  "filter=all returns all groups, no summary-groups."
+  (let* ((model (spine-index-model spine-index-model-test--books "all"))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should-not summaries)
+    (should (member "on deck" group-labels))
+    (should (member "reading" group-labels))
+    (should (member "read" group-labels))
+    (should (= (length groups) 3))))  ; WANT, READING, READ (no ABANDONED in sample)
+```
+
+- [ ] **Step 6: Write test — filter=read returns only READ group**
+
+```elisp
+(ert-deftest spine-index-model-filter-read-returns-only-read ()
+  "filter=read returns only the READ group."
+  (let* ((model (spine-index-model spine-index-model-test--books "read"))
+         (groups (ht-get model "groups")))
+    (should (= (length groups) 1))
+    (should (string= (ht-get (car groups) "label") "read"))
+    (should (= (ht-get (car groups) "count") 1))))
+```
+
+- [ ] **Step 7: Write test — filter=want returns only WANT group**
+
+```elisp
+(ert-deftest spine-index-model-filter-want-returns-only-want ()
+  "filter=want returns only the WANT group."
+  (let* ((model (spine-index-model spine-index-model-test--books "want"))
+         (groups (ht-get model "groups")))
+    (should (= (length groups) 1))
+    (should (string= (ht-get (car groups) "label") "on deck"))
+    (should (= (ht-get (car groups) "count") 3))))
+```
+
+- [ ] **Step 8: Write test — invalid filter falls back to concise**
+
+```elisp
+(ert-deftest spine-index-model-invalid-filter-falls-back-to-concise ()
+  "Unrecognised filter value behaves like nil (concise view)."
+  (let* ((model (spine-index-model spine-index-model-test--books "bogus"))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should summaries)                            ; has summary
+    (should-not (member "read" group-labels))     ; no read group
+    (should (member "reading" group-labels))      ; has reading
+    (should (member "on deck" group-labels))))    ; has want
+```
+
+- [ ] **Step 9: Write test — model includes current_filter in context**
+
+```elisp
+(ert-deftest spine-index-model-includes-current-filter ()
+  "Model includes :current_filter key matching the filter argument."
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books) "current_filter") ""))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "all") "current_filter") "all"))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "read") "current_filter") "read"))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "want") "current_filter") "want")))
+```
+
+- [ ] **Step 10: Run tests to verify they fail**
+
+```bash
+cd /work/personal-local/spine
+emacs --batch -l test/spine-index-model-test.el \
+  --eval "(ert-run-tests-batch-and-exit '(not (tag :unstable)))" 2>&1
+```
+
+Expected: all tests fail because `spine-index-model` doesn't accept a second argument yet.
+
+- [ ] **Step 11: Commit test file**
+
+```bash
+git add test/spine-index-model-test.el
+git commit -m "test: add failing tests for filtered spine-index-model"
+```
+
+---
+
+### Task 2: Implement filtered `spine-index-model`
+
+**Files:**
+- Modify: `spine.el:77-155`
+
+- [ ] **Step 1: Update signature and add filter handling**
+
+Swap the function at line 77:
+
+```elisp
+(defun spine-index-model (books &optional filter selected-id)
+  "Build the view model ht for templates/index.mustache from BOOKS.
+FILTER controls which books are shown:
+  nil      — concise: READING + 5 most recent WANT, others as summary links
+  \"all\"   — full listing, no truncation
+  \"read\"  — only READ books
+  \"want\"  — only WANT books
+SELECTED-ID expands the matching book's detail section."
+  (let* ((status-labels
+          '(("WANT"      . "on deck")
+            ("READING"   . "reading")
+            ("READ"      . "read")
+            ("ABANDONED" . "abandoned")))
+         (format-icons
+          '(("hardcover"  . "ti-book")
+            ("ebook"     . "ti-device-tablet")
+            ("audiobook" . "ti-headphones")))
+         (order '("WANT" "READING" "READ" "ABANDONED"))
+         (valid-filters '("all" "read" "want"))
+         (effective-filter (if (member filter valid-filters) filter nil))
+         (grouped (make-hash-table :test 'equal))
+         (total (length books))
+         (reading-count 0))
+    (dolist (book books)
+      (when (equal "READING" (plist-get book :status))
+        (cl-incf reading-count)))
+    (dolist (book books)
+      (let ((status (or (plist-get book :status) "WANT")))
+        (push book (gethash status grouped))))
+    (let ((groups nil)
+          (summary-groups nil))
+      (dolist (status order)
+        (let ((group-books (nreverse (gethash status grouped))))
+          (when group-books
+            (if (and (null effective-filter)
+                     (member status '("READ" "ABANDONED")))
+                ;; Concise: replace read/abandoned groups with summary links
+                (push (ht ("label" (cdr (assoc status status-labels)))
+                          ("count" (length group-books))
+                          ("href" (format "/index?filter=%s"
+                                          (downcase status))))
+                      summary-groups)
+              ;; Show the group (possibly filtered to one status)
+              (when (or (null effective-filter)
+                        (string= (downcase status) effective-filter)
+                        (string= effective-filter "all"))
+                ;; Sort WANT by ADDED descending when in concise view
+                (when (and (null effective-filter)
+                           (string= status "WANT"))
+                  (setq group-books
+                        (cl-subseq (sort group-books
+                                         (lambda (a b)
+                                           (let ((a-date (plist-get a :added))
+                                                 (b-date (plist-get b :added)))
+                                             (cond
+                                              ((null a-date) nil)
+                                              ((null b-date) t)
+                                              (t (string> a-date b-date))))))
+                                   0 (min (length group-books) 5))))
+                (let ((book-models nil))
+                  (dolist (book group-books)
+                    (let* ((id (plist-get book :id))
+                           (selected (equal id selected-id))
+                           (fmt (plist-get book :format))
+                           (rating (plist-get book :rating))
+                           (notes (plist-get book :notes))
+                           (status (or (plist-get book :status) "WANT"))
+                           (model
+                            (ht
+                             ("format_icon"
+                              (or (cdr (assoc fmt format-icons)) ""))
+                             ("status_class" (downcase status))
+                             ("status_label" (downcase status))
+                             ("title" (plist-get book :title))
+                             ("author" (or (plist-get book :author) ""))
+                             ("tags_inline"
+                              (let ((tags (plist-get book :tags)))
+                                (when tags
+                                  (mapconcat (lambda (tag) (concat ":" tag ":"))
+                                             tags " "))))
+                             ("rec_via" (plist-get book :rec_by))
+                             ("rating_display"
+                              (when (and rating (> (length rating) 0))
+                                (make-string (string-to-number rating) ?\u2605)))
+                             ("selected" selected)
+                             ("detail"
+                              (when selected
+                                (ht
+                                 ("meta"
+                                  (let ((added (plist-get book :added))
+                                        (fmt (plist-get book :format)))
+                                    (cond
+                                     ((and added fmt)
+                                      (format "started %s · %s" added fmt))
+                                     (added (format "started %s" added))
+                                     (fmt (format "format: %s" fmt))
+                                     (t ""))))
+                                 ("notes"
+                                  (when notes
+                                    (cl-loop for (date text) in notes
+                                             collect (ht
+                                                      ("date" (format "[%s]" date))
+                                                      ("text" text)))))))))))
+                      (push model book-models)))
+                  (push (ht ("label" (cdr (assoc status status-labels)))
+                            ("count" (length group-books))
+                            ("books" (nreverse book-models)))
+                        groups))))))
+      (ht ("app_title" "spine")
+          ("total_books" total)
+          ("reading_count" reading-count)
+          ("current_filter" (or effective-filter ""))
+          ("summary_groups" (nreverse summary-groups))
+          ("groups" (nreverse groups))))))
+```
+
+- [ ] **Step 2: Run tests to verify they pass**
+
+```bash
+cd /work/personal-local/spine
+emacs --batch -l test/spine-index-model-test.el \
+  -l test/spine-books-test.el \
+  -l test/spine-add-book-test.el \
+  --eval "(ert-run-tests-batch-and-exit '(not (tag :unstable)))" 2>&1
+```
+
+Expected: all tests pass (new filter tests + existing books + add-book tests).
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add spine.el
+git commit -m "feat: add filter parameter to spine-index-model for concise default view"
+```
+
+---
+
+### Task 3: Update `defservlet index` handler
+
+**Files:**
+- Modify: `spine.el:308-313`
+
+- [ ] **Step 1: Pass query filter to model**
+
+Swap lines 308-313:
+
+```elisp
+(defservlet index text/html (path query request)
+  (let* ((books (spine-books))
+         (filter (cadr (assoc "filter" query))))
+    (if books
+        (insert (spine-render "index.mustache"
+                  (spine-index-model books filter (cadr (assoc "id" query)))))
+      (insert (spine-render-empty-state)))))
+```
+
+- [ ] **Step 2: Run existing tests to confirm handler change doesn't break anything**
+
+```bash
+cd /work/personal-local/spine
+emacs --batch -l test/spine-index-model-test.el \
+  -l test/spine-books-test.el \
+  -l test/spine-add-book-test.el \
+  --eval "(ert-run-tests-batch-and-exit '(not (tag :unstable)))" 2>&1
+```
+
+Expected: all pass.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add spine.el
+git commit -m "feat: pass filter query param from index handler to model"
+```
+
+---
+
+### Task 4: Update `templates/index.mustache` with filter links and summary groups
+
+**Files:**
+- Modify: `templates/index.mustache`
+
+- [ ] **Step 1: Add filter nav bar after header, before groups**
+
+Insert after the closing `</header>` (line 87) and before the `{{#groups}}` section (line 89):
+
+```mustache
+    {{#current_filter}}
+    <nav class="filter-bar" style="padding: .4rem .9rem; font-size: .8rem;">
+      <a href="/index">Concise view</a>
+    </nav>
+    {{/current_filter}}
+    {{^current_filter}}
+    <nav class="filter-bar" style="padding: .4rem .9rem; font-size: .8rem;">
+      <span>
+        <a href="/index?filter=all">All books ({{total_books}})</a>
+        &nbsp;·&nbsp;
+        <a href="/index?filter=want">Want list</a>
+        &nbsp;·&nbsp;
+        <a href="/index?filter=read">Read ({{reading_count}})</a>
+      </span>
+    </nav>
+    {{/current_filter}}
+```
+
+- [ ] **Step 2: Add summary group rows after groups section**
+
+Insert after the closing `{{/groups}}` (line 109) and before `<div class="endpad">` (line 110):
+
+```mustache
+    {{#summary_groups}}
+    <div class="row"><a href="{{href}}">{{label}} · {{count}}</a></div>
+    {{/summary_groups}}
+```
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add templates/index.mustache
+git commit -m "feat: add filter nav bar and summary group links to index template"
+```
+
+---
+
+### Task 5: Manual integration test
+
+- [ ] **Step 1: Start the server and verify concise default view**
+
+```bash
+cd /work/personal-local/spine
+SPINE_ORG_FILE=$(pwd)/sample-books.org emacs --batch -l spine.el \
+  --eval "(setq spine-org-file \"$(pwd)/sample-books.org\")" \
+  --eval "(httpd-start)" \
+  --eval "(message \"Server running on port 8080\")" &
+sleep 2
+curl -s http://localhost:8080/index | head -50
+```
+
+Verify the output:
+- Shows READING group (Use of Weapons)
+- Shows WANT group (Piranesi, Dune, Left Hand)
+- Does NOT show READ group (Ancillary Justice) as a full group
+- Shows a summary link for "read · 1"
+- Shows "All books (5)" filter nav link
+
+- [ ] **Step 2: Test filter=all**
+
+```bash
+curl -s "http://localhost:8080/index?filter=all"
+```
+
+Verify: all books shown in their groups, no summary sections, "Concise view" link present.
+
+- [ ] **Step 3: Test filter=read**
+
+```bash
+curl -s "http://localhost:8080/index?filter=read"
+```
+
+Verify: only Ancillary Justice shown, "Concise view" link present.
+
+- [ ] **Step 4: Kill the server**
+
+```bash
+kill %1 2>/dev/null; wait 2>/dev/null
+```
+
+- [ ] **Step 5: Run all tests one final time**
+
+```bash
+cd /work/personal-local/spine
+emacs --batch -l test/spine-index-model-test.el \
+  -l test/spine-books-test.el \
+  -l test/spine-add-book-test.el \
+  --eval "(ert-run-tests-batch-and-exit '(not (tag :unstable)))" 2>&1
+```
+
+Expected: all pass.
+
+- [ ] **Step 6: Final commit if any fixes needed**
+
+```bash
+git commit -am "fix: address integration test findings"
+```

docs/specs/2026-06-21-concise-default-view-design.md

@@ -0,0 +1,97 @@
+# Concise Default View — design spec
+
+## Problem
+
+The index page shows every book grouped by status. As the library grows, this becomes
+too much information at a glance. The user needs a focused default showing only what's
+active right now, with easy paths to browse the rest.
+
+## Design
+
+The index view takes an optional `filter` query parameter. With no filter, it shows a
+concise default: only books in-flight (READING) and the 5 most recently added WANT
+books. All other books are accessible via filter links. With a filter (`all`, `read`,
+`want`), it shows the full matching subset.
+
+## Behaviour
+
+### Default / no filter (concise view)
+
+- **READING group**: all READING books (unchanged from current).
+- **WANT group**: sorted by `:ADDED:` date descending, limited to 5.
+- **READ / ABANDONED**: replaced by summary links — e.g. "Read · 3" as a clickable
+  link to `/index?filter=read`.
+- **Filter nav bar** shown at the top: links to `All books (N)`, `Want list`,
+  `Read (N)`.
+
+### `?filter=all`
+
+Full index, all groups, no truncation — identical to today's default.
+
+### `?filter=read`
+
+Only the READ group. Single group in the listing.
+
+### `?filter=want`
+
+Only the WANT group. Single group in the listing.
+
+### Error handling
+
+- An unrecognised/empty filter value is treated as `nil` (concise default).
+- A WANT book with no `:ADDED:` property sorts before dated entries (treated as
+  oldest).
+- Fewer than 5 WANT books → all are shown, no padding or placeholder rows.
+
+## Implementation
+
+### Model: `spine-index-model`
+
+Signature changes from:
+```
+spine-index-model (books &optional selected-id)
+```
+to:
+```
+spine-index-model (books &optional filter selected-id)
+```
+
+When `filter` is nil, after building the group alist:
+- Sort the `:want` group entries by `added` descending (ISO date string; nils sort
+  first = oldest).
+- Truncate to 5 entries.
+- Replace `:read` and `:abandoned` groups with a `:summary-groups` list. Each
+  entry is a plist matching the existing model convention:
+  ```
+  (:label "read" :count 3 :href "/index?filter=read")
+  ```
+  The template renders these as clickable `.row` links.
+  When `filter` is non-nil, `:summary-groups` is absent.
+When `filter` is non-nil, return only the matching group (or all groups for `"all"`).
+
+### Handler: `defservlet index`
+
+Read the `filter` key from the request query alist. Pass it to `spine-index-model`.
+Pass `current_filter` in the template context for conditional rendering.
+
+### Template: `index.mustache`
+
+- **Filter bar** (above groups): shown when `current_filter` is nil (links to expanded
+  views) or truthy (link back to concise view).
+- **Summary groups**: new `{{#summary_groups}}` block renders a simple `.row` link per
+  suppressed group (READ, ABANDONED).
+- Existing group rendering unchanged — still handles full listing when `filter=all`
+  or single-group views.
+
+### Sorting
+
+Within the WANT group for the concise view: sort by `added` field descending. The
+`added` field is already part of each book's model entry. Nil dates sort before dated
+entries (oldest).
+
+## Out of scope
+
+- Pagination for large WANT lists (5 is a design choice; if the user wants more, the
+  "All books" link is there).
+- Remembering the user's last selected filter across requests (stateless is simpler).
+- Keyboard-driven filter switching (plain links for now).

spine.el

@@ -74,8 +74,13 @@ Returns the rendered string."
         ("existing_authors" (sort authors #'string<))
         ("existing_categories" (sort categories #'string<)))))
 
-(defun spine-index-model (books &optional selected-id)
+(defun spine-index-model (books &optional filter selected-id)
   "Build the view model ht for templates/index.mustache from BOOKS.
+FILTER controls which books are shown:
+  nil      - concise: READING + 5 most recent WANT, others as summary links
+  all   - full listing, no truncation
+  read  - only READ books
+  want  - only WANT books
 SELECTED-ID expands the matching book's detail section."
   (let* ((status-labels
           '(("WANT"      . "on deck")
@@ -87,6 +92,8 @@ SELECTED-ID expands the matching book's detail section."
             ("ebook"     . "ti-device-tablet")
             ("audiobook" . "ti-headphones")))
          (order '("WANT" "READING" "READ" "ABANDONED"))
+         (valid-filters '("all" "read" "want"))
+         (effective-filter (if (member filter valid-filters) filter nil))
          (grouped (make-hash-table :test 'equal))
          (total (length books))
          (reading-count 0))
@@ -96,10 +103,33 @@ SELECTED-ID expands the matching book's detail section."
     (dolist (book books)
       (let ((status (or (plist-get book :status) "WANT")))
         (push book (gethash status grouped))))
-    (let ((groups nil))
+    (let ((groups nil)
+          (summary-groups nil))
       (dolist (status order)
         (let ((group-books (nreverse (gethash status grouped))))
           (when group-books
+            (if (and (null effective-filter)
+                     (member status '("READ" "ABANDONED")))
+                (push (ht ("label" (cdr (assoc status status-labels)))
+                          ("count" (length group-books))
+                          ("href" (format "/index?filter=%s"
+                                          (downcase status))))
+                      summary-groups)
+              (when (or (null effective-filter)
+                        (string= (downcase status) effective-filter)
+                        (string= effective-filter "all"))
+                (when (and (null effective-filter)
+                           (string= status "WANT"))
+                  (setq group-books
+                        (cl-subseq (sort group-books
+                                         (lambda (a b)
+                                           (let ((a-date (plist-get a :added))
+                                                 (b-date (plist-get b :added)))
+                                             (cond
+                                              ((null a-date) nil)
+                                              ((null b-date) t)
+                                              (t (string> a-date b-date))))))
+                                   0 (min (length group-books) 5))))
                 (let ((book-models nil))
                   (dolist (book group-books)
                     (let* ((id (plist-get book :id))
@@ -134,7 +164,7 @@ SELECTED-ID expands the matching book's detail section."
                                         (fmt (plist-get book :format)))
                                     (cond
                                      ((and added fmt)
-                                  (format "started %s · %s" added fmt))
+                                      (format "started %s \302\267 %s" added fmt))
                                      (added (format "started %s" added))
                                      (fmt (format "format: %s" fmt))
                                      (t ""))))
@@ -148,12 +178,13 @@ SELECTED-ID expands the matching book's detail section."
                   (push (ht ("label" (cdr (assoc status status-labels)))
                             ("count" (length group-books))
                             ("books" (nreverse book-models)))
-                    groups)))))
+                        groups)))))))
       (ht ("app_title" "spine")
           ("total_books" total)
           ("reading_count" reading-count)
+          ("current_filter" effective-filter)
+          ("summary_groups" (nreverse summary-groups))
           ("groups" (nreverse groups))))))
-
 (defun spine-add-book (&rest args)
   "Add a new WANT book to `spine-org-file'.
 Keyword arguments: :title :author :category :format :isbn :cover
@@ -306,10 +337,11 @@ Set by test harnesses that only need the model functions.")
 ;; --- handlers ---------------------------------------------------------
 
 (defservlet index text/html (path query request)
-  (let ((books (spine-books)))
+  (let* ((books (spine-books))
+         (filter (cadr (assoc "filter" query))))
     (if books
         (insert (spine-render "index.mustache"
-                  (spine-index-model books (cadr (assoc "id" query)))))
+                  (spine-index-model books filter (cadr (assoc "id" query)))))
       (insert (spine-render-empty-state)))))
 
 (defun httpd/add (proc uri-path query request)

templates/index.mustache

@@ -86,6 +86,23 @@
       </nav>
     </header>
 
+    {{#current_filter}}
+    <nav class="filter-bar" style="padding: .4rem .9rem; font-size: .8rem;">
+      <a href="/index">Concise view</a>
+    </nav>
+    {{/current_filter}}
+    {{^current_filter}}
+    <nav class="filter-bar" style="padding: .4rem .9rem; font-size: .8rem;">
+      <span>
+        <a href="/index?filter=all">All books ({{total_books}})</a>
+        &nbsp;·&nbsp;
+        <a href="/index?filter=want">Want list</a>
+        &nbsp;·&nbsp;
+        <a href="/index?filter=read">Read ({{reading_count}})</a>
+      </span>
+    </nav>
+    {{/current_filter}}
+
     {{#groups}}
     <div class="group">{{label}} · {{count}}</div>
     {{#books}}
@@ -107,6 +124,9 @@
     {{/detail}}
     {{/books}}
     {{/groups}}
+    {{#summary_groups}}
+    <div class="row"><a href="{{href}}">{{label}} · {{count}}</a></div>
+    {{/summary_groups}}
     <div class="endpad"></div>
 
     {{#minibuffer}}

test/spine-index-model-test.el

@@ -0,0 +1,103 @@
+;;; spine-index-model-test.el — ERT tests for spine-index-model with filter
+
+(require 'ert)
+(require 'cl-lib)
+
+(setq spine-skip-server-start t)
+(setq spine-org-file (expand-file-name "sample-books.org"
+                                       (file-name-directory
+                                        (directory-file-name
+                                         (file-name-directory load-file-name)))))
+(load-file (expand-file-name "../spine.el"
+                             (file-name-directory load-file-name)))
+
+(defconst spine-index-model-test--books (spine-books)
+  "Books fixture loaded once from sample-books.org.")
+
+(ert-deftest spine-index-model-concise-hides-read-and-abandoned ()
+  "Concise view (filter=nil) omits READ/ABANDONED groups, adds summary-groups."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should-not (member "read" group-labels))
+    (should-not (member "abandoned" group-labels))
+    (should summaries)
+    (should (= (length summaries) 1))
+    (should (string= (ht-get (car summaries) "label") "read"))
+    (should (= (ht-get (car summaries) "count") 1))
+    (should (string= (ht-get (car summaries) "href") "/index?filter=read"))))
+
+(ert-deftest spine-index-model-concise-includes-reading ()
+  "Concise view includes READING group with all reading books."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (reading-group (cl-find "reading" groups
+                                 :key (lambda (g) (ht-get g "label"))
+                                 :test #'string=)))
+    (should reading-group)
+    (should (= (ht-get reading-group "count") 1))
+    (should (string= (ht-get (car (ht-get reading-group "books")) "title")
+                     "Use of Weapons"))))
+
+(ert-deftest spine-index-model-concise-want-limited-to-five ()
+  "Concise view limits WANT group to 5 books, sorted by :ADDED: desc."
+  (let* ((model (spine-index-model spine-index-model-test--books))
+         (groups (ht-get model "groups"))
+         (want-group (cl-find "on deck" groups
+                              :key (lambda (g) (ht-get g "label"))
+                              :test #'string=)))
+    (should want-group)
+    (let ((books (ht-get want-group "books")))
+      (should (<= (length books) 5))
+      (should (= (length books) 3))
+      ;; Piranesi (2026-06-01), Dune (2026-05-10), Left Hand (2026-04-01)
+      (should (string= (ht-get (nth 0 books) "title") "Piranesi"))
+      (should (string= (ht-get (nth 1 books) "title") "Dune"))
+      (should (string= (ht-get (nth 2 books) "title") "The Left Hand of Darkness")))))
+
+(ert-deftest spine-index-model-filter-all-shows-all-groups ()
+  "filter=all returns all groups, no summary-groups."
+  (let* ((model (spine-index-model spine-index-model-test--books "all"))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should-not summaries)
+    (should (member "on deck" group-labels))
+    (should (member "reading" group-labels))
+    (should (member "read" group-labels))
+    (should (= (length groups) 3))))
+
+(ert-deftest spine-index-model-filter-read-returns-only-read ()
+  "filter=read returns only the READ group."
+  (let* ((model (spine-index-model spine-index-model-test--books "read"))
+         (groups (ht-get model "groups")))
+    (should (= (length groups) 1))
+    (should (string= (ht-get (car groups) "label") "read"))
+    (should (= (ht-get (car groups) "count") 1))))
+
+(ert-deftest spine-index-model-filter-want-returns-only-want ()
+  "filter=want returns only the WANT group."
+  (let* ((model (spine-index-model spine-index-model-test--books "want"))
+         (groups (ht-get model "groups")))
+    (should (= (length groups) 1))
+    (should (string= (ht-get (car groups) "label") "on deck"))
+    (should (= (ht-get (car groups) "count") 3))))
+
+(ert-deftest spine-index-model-invalid-filter-falls-back-to-concise ()
+  "Unrecognised filter value behaves like nil (concise view)."
+  (let* ((model (spine-index-model spine-index-model-test--books "bogus"))
+         (groups (ht-get model "groups"))
+         (summaries (ht-get model "summary_groups"))
+         (group-labels (mapcar (lambda (g) (ht-get g "label")) groups)))
+    (should summaries)
+    (should-not (member "read" group-labels))
+    (should (member "reading" group-labels))
+    (should (member "on deck" group-labels))))
+
+(ert-deftest spine-index-model-includes-current-filter ()
+  "Model includes current_filter key matching the filter argument."
+  (should (not (ht-get (spine-index-model spine-index-model-test--books) "current_filter")))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "all") "current_filter") "all"))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "read") "current_filter") "read"))
+  (should (equal (ht-get (spine-index-model spine-index-model-test--books "want") "current_filter") "want")))