Add connect mode, portals, backlinks and renames (stage 8d, v1)

Part 8d, the last of stage 8, and with it everything on DESIGN.md's v1
list.

Connect mode (C): the cursor goes to another node, a dashed arrow in the
visual color follows it, and Enter links the two; then the cursor goes
back to where C was typed (the user's pick). d removes the line between
them (a branch is cut, and the child comes loose), > puts the node under
the other one, and <Space> a, l, c, s and t style the line as you watch,
making it when it isn't there yet. Everything connect mode changes is one
undo group, and Esc takes it back with History::cancel, which leaves
nothing to redo. From visual mode every selected node connects, and the
line pickers go back to connect mode when they close.

Portals show their document live, from a cache of what each document
file holds (open documents from their buffers, the others from their
files, looked at every second): the root's title, its color and how many
nodes it has, or ? when the document isn't there. Enter or gf goes
through, as a jump, and the pane's breadcrumb starts with the documents
it came through. <Space>p types :portal (the user's pick): a path as :e
takes it, or the title of a new document. Backlinks are put right
whenever a document is opened or saved; the root shows how many, the
Note view lists them, gu goes up to them (the user's pick) and
:backlinks lists them.

File names follow the root's title: when it changed, the next save
renames the file (-2 when the name is taken; a folder's default document
keeps its name), and the portals pointing at it, its backlinks in the
documents it leads to, the recent documents, the capital marks and the
jump lists follow. A portal whose file was moved by hand finds its
document in that folder by uid. Portals in a register keep full paths,
so a pasted portal leads to the same document from any folder.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

DESIGN.md

@@ -197,6 +197,58 @@ lines.
   beside the node. `:marks`, `:jumps` and `:registers` list them; Enter goes
   to the mark or the place, or pastes the register.
 
+**Connect mode and portals** (settled in part 8d)
+- `C` starts connect mode on the cursor's node: the cursor goes to another
+  node as usual (`hjkl`, `gh`…, `n` after a search, a click), the node
+  being connected is drawn thick in the visual color, and a dashed arrow in
+  that color follows the cursor. Enter links them (a line already there
+  stays) and connect mode is done, with the cursor back on the node `C`
+  started from (the user's pick). `d` removes the line between them: a link
+  goes; a branch (aimed at the node's parent, or at a child) is cut, and the
+  child comes loose with its own branch. `>` puts the node under the one
+  aimed at, as its last child, where it is on the canvas (a link between the
+  two goes: the branch takes its place).
+- The `<Space>` keys style the line as you watch: `a` and `l` go through the
+  arrowheads (off, end, start, both) and the kinds of line (solid, dashed,
+  dotted, thick, double); `c` and `s` pick a color (or the node's own) and a
+  named line style; `t` a link's label, where typing a label that isn't
+  listed makes it. A line that isn't there yet is made, as a link. Everything
+  connect mode changes is one undo step, and Esc takes it all back.
+- From visual mode, `C` connects every selected node (with `V`, each
+  branch's top) to the one the cursor goes to. Connect mode works in every
+  view, and stays in its document.
+- A portal shows its document live: the root's title, its color (when the
+  portal has none of its own) and how many nodes it has, in the box's corner
+  (`?` and faded when the document isn't there). The portal remembers the
+  title, in case the file goes. Enter or `gf` goes through it, to the root:
+  a jump, so `Ctrl-o` comes back. The breadcrumb then starts with the
+  documents the pane came through (`Garden plans » Kitchen › Herbs`);
+  going back up one of them takes the trail back there.
+- `<Space>p` opens the command line with `:portal ` typed (the user's
+  pick): a path as `:e` takes it, relative to the document's folder, with
+  the same completion. An existing document gets a portal under the
+  cursor's node, where `a` adds a child; when nothing's there, what was
+  typed is a new document's title, made next to this one as `:new` makes
+  it. A portal to its own document, or to a file that isn't a document, is
+  refused.
+- Backlinks are put right whenever a document is opened or saved: each
+  document its portals lead to gets exactly one backlink per portal (an
+  open one in its buffer, written at once unless it has changes of its own
+  to save with them; a closed one in its file, unless another cumulus has
+  it). The root shows how many (`« 2`), the Note view lists them on the
+  root, and `gu` goes up to them (the user's pick): one straight there, on
+  the portal, several in a list, the document the pane came from first.
+  `:backlinks` always lists them.
+- File names follow the root's title: when the title changed since the
+  file was read or written, the next save renames it (`-2`, `-3`… when the
+  name is taken; a folder's default document keeps its name). The portals
+  pointing at it take the new path (in the documents its backlinks name,
+  and any open one), as do the backlinks in the documents it leads to, the
+  recent documents, the capital marks and the jump lists.
+- A portal whose file isn't where it says looks in that folder for its
+  document by uid (a file moved or renamed by hand), and keeps the path it
+  finds.
+
 **Views, panes and popups** (settled in stage 7)
 - The Note view is made of parts: the title, the tags, the body, each link
   (out, then in) and each child. `j` and `k` step through them, with a bar
@@ -406,7 +458,8 @@ enum Mode {
                           // two can't disagree. Rapid entry lives here too.
     Visual(Visual),       // anchor + Rectangle or Branches
     Move(Grab),           // a node or a branch being moved
-    Connect(Connect),     // the source node and the link being styled
+    Connect(Connect),     // the nodes being connected, where the cursor goes
+                          // back, and the undo group Esc takes back
     Command(CommandLine), // `:` with completion
     Popup(Popup),         // the help, the menu, a picker or the K card (which
                           // holds its own TextEdit while the body is edited)
@@ -420,12 +473,12 @@ text).
 
 | Group | Keys |
 |---|---|
-| **Move** (every view) | `hjkl` or arrows · `gh gj gk gl` tree moves · `w` `b` next / previous in reading order · `gg` root · `G` last · `/` `n` `N` search · `Ctrl-o` `Ctrl-i` (Tab) jump back / forward · `m{a-z}` `'{a-z}` marks (`A–Z` across documents) · Enter or `gf` through a portal · `gd` follow a cross-link |
+| **Move** (every view) | `hjkl` or arrows · `gh gj gk gl` tree moves · `w` `b` next / previous in reading order · `gg` root · `G` last · `/` `n` `N` search · `Ctrl-o` `Ctrl-i` (Tab) jump back / forward · `m{a-z}` `'{a-z}` marks (`A–Z` across documents) · Enter or `gf` through a portal · `gu` up to the portals that lead here · `gd` follow a cross-link |
 | **View** | `zz` center · `Ctrl-e` `Ctrl-y` `zh` `zl` pan · `Ctrl-d` `Ctrl-u` half a screen · `+` `-` zoom · `za zo zc zR zM` folds · `zf` Auto · `zi` focus · `K` body card |
 | **Create and edit** | `o` `O` sibling below / above · `a` child · `i` `A` Enter edit the title · `I` edit from its start · `cc` `S` retype |
 | **Operators** | `dd` or `dab` delete branch · `dib` delete children · `x` delete just the node · `yy` `yab` `yib` yank · `p` paste as children · `P` paste as siblings below · `>>` `<<` indent / outdent · `"a`–`"z` and `"+` registers · `.` repeat · `u` `Ctrl-r` undo / redo |
 | **Modes** | `v` `V` visual · `M` move · `C` connect · `:` command · Esc back to normal |
-| **Leader** `<Space>` | `c` color · `s` style · `B` border · `t` tags · `p` new portal · `i` inbox · `b` documents · `v` then `c`/`o`/`n` for canvas / outline / note · `w` which-key on/off · `?` help |
+| **Leader** `<Space>` | `c` color · `s` style · `B` border · `t` tags · `p` new portal (`:portal `) · `i` inbox · `b` documents · `v` then `c`/`o`/`n` for canvas / outline / note · `w` which-key on/off · `?` help |
 | **Panes, documents** | `Ctrl-w v` `Ctrl-w s` split · `Ctrl-w hjkl` focus · `Ctrl-w w` the next pane · `Ctrl-w c` close · `Ctrl-w o` only · `Ctrl-w =` even sizes · `gt` `gT` `]b` `[b` next / previous document · `ZZ` close pane (the last one quits) |
 | **Outline** | `j` `k` rows · `h` `l` parent / first child · `zb` every body · `M` then `j` `k` (`J` `K`: 5) swap with siblings, `h` out, `l` under the one above |
 | **Note view** | `j` `k` parts · Enter `i` `A` edit the part (`I` from its start, `cc` `S` anew), or go to that link or child · `h` `l` the sibling before / after |
@@ -434,7 +487,7 @@ text).
 | **Typing** | `Backspace` `Delete` · `Ctrl-w` delete word · `Ctrl-u` delete line · arrows, Home, End · Enter (title: done, or after `o O a` the next idea; body: new line) · Tab Shift-Tab (a new idea: under the one above / out a level) · Esc to vim keys |
 | **Inside text** | `h j k l w b e 0 ^ $ gg G` (and arrows, Home, End) · `f t F T ; ,` · `d` `c` `y` with any motion and `iw aw i" a" i( a(` · `x X s S D C Y` · `r ~ J p P` · `u Ctrl-r .` · `i a I A` back to typing · `o O` (title: a new sibling; body: a new line) · Esc done |
 | **Move mode** | `hjkl` 1 cell · `HJKL` 5 cells · `M` branch ↔ node · Enter or Esc done |
-| **Connect mode** | move to the target as usual · Enter link · `d` remove · `>` attach as child · `<Space>` style menu (`s` named, `a` arrows, `l` line, `c` color, `t` label) · Esc cancel |
+| **Connect mode** | move to the target as usual (or click it) · Enter link · `d` remove (a branch: cut) · `>` attach as child · `<Space>` style menu (`s` named, `a` arrows, `l` line, `c` color, `t` label) · Esc cancel (takes it all back) |
 | **Visual** | `d` `x` `y` `>` `<` `M` and `<Space>c` `<Space>s` `<Space>B` `<Space>t` act on the whole selection · `o` swaps ends · `v` `V` switch, or stop · Ctrl+click, Ctrl+drag pick with the mouse |
 
 ## Files
@@ -616,9 +669,9 @@ cumulus/
    │               command_line, theme, glyphs
    ├─ config/      paths (the config and data folders), settings (config.toml, `:set`), keys_file
    │               (keys.toml's template), theme_file (themes laid over the built-in one)
-   ├─ storage/     document_file (RON), write_atomically, names (file names from titles), backup,
-   │               lock, stamp (noticing changes made outside), memory (memory.ron), markdown
-   │               (nodes as Markdown, for the clipboard)
+   ├─ storage/     document_file (RON), write_atomically, names (file names from titles), link_paths
+   │               (portal paths: relative, with /), backup, lock, stamp (noticing changes made
+   │               outside), memory (memory.ron), markdown (nodes as Markdown, for the clipboard)
    └─ app/         mod.rs (App), input (keys and the mouse, routed), update (carrying actions out),
                    render, terminal (the main loop, setup, teardown, panic hook), startup (what
                    `cumulus` opens), documents (the open documents and their files), files
@@ -628,12 +681,14 @@ cumulus/
                    edited, rapid entry), registers (text or nodes), clipboard (the system's, for
                    "+), yank (nodes into registers and back), visual (selections), repeat (`.`),
                    search (`/`), jumps (each pane's jump list), marks (capital marks, `:marks`),
-                   panes (the split tree), popup (help, menu, pickers, card, questions); later
-                   portals (cache, backlinks, renames)
+                   connect (connect mode), portals (what portals show, going through them,
+                   `:portal`, backlinks, renames), panes (the split tree), popup (help, menu,
+                   pickers, card, questions)
 ```
 
 The end-to-end tests are in `app/tests.rs` (with `app/tests/files.rs`,
-`app/tests/config.rs` and `app/tests/vim.rs`): they copy the sample
+`app/tests/config.rs`, `app/tests/vim.rs`, `app/tests/connect.rs` and
+`app/tests/portals.rs`): they copy the sample
 documents to a temporary folder, type keys and click on a test terminal, and
 check the screen, the documents and the files.