Add problems-only view (!) and draft the write actions

`!` reduces the tree to submodules with issues (or unknown state) plus
their ancestors, reusing the filter's reduction. Adds docs/actions.md as
a draft spec for restore and stage pin.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -109,6 +109,7 @@ files.
 | `space` | Toggle the selected submodule |
 | `home` `end` / `g` `G`, `pgup` `pgdn` | Jump, page |
 | `/` | Filter |
+| `!` | Problems only |
 | `c` | Copy path |
 | `f` / `r` | Fetch / reload |
 | `?` | Full help |
@@ -118,8 +119,8 @@ The mouse works too: click to select, click `▸` to toggle, wheel to move.
 
 ## Status
 
-A prototype. Browsing is complete; the actions `u` (check out the pin),
-`b` (bump the pin to the tip) and `!` (problems only) are planned.
+A prototype. Browsing is complete; the actions `u` (check out the pin) and `b` (bump the pin to the tip) are
+planned.
 
 ## Documentation
 

docs/README.md

@@ -14,6 +14,7 @@ bare commit hash.
 | [state-model.md](state-model.md) | How a submodule's state is determined, summarized into issues, and how pins are resolved to refs |
 | [ux-guide.md](ux-guide.md) | Layout, attention hierarchy, colors, wording, navigation and key bindings |
 | [architecture.md](architecture.md) | Package layout, the provider boundary, async loading, testing |
+| [actions.md](actions.md) | **Draft:** the write actions restore and stage pin |
 | [decisions.md](decisions.md) | Decision log with rationale (ADR style) |
 
 ## Install
@@ -32,10 +33,11 @@ Installs `submarine` and the alias `sub` (linux/macOS, amd64/arm64) to
 through a git provider (`internal/submodule/git`): `submarine [dir]`. It
 fetches in the background on startup (`--no-fetch` to skip; `f` to fetch
 again) and follows changes made in other shells. `submarine --mock` shows
-the built-in mock data (`internal/submodule/mock`). The actions `u`, `b`,
-`!` only show a "not implemented" message.
+the built-in mock data (`internal/submodule/mock`). `!` shows only
+submodules with problems. The actions `u` and `b` only show a "not
+implemented" message ([drafts of the write actions](actions.md)).
 
 Next steps, roughly in order:
 
 1. Actions: checkout pin (`submodule update`), bump pin to tip, init.
-2. "Problems only" (`!`) view; it can reuse the tree's filter.
+2. (done) "Problems only" (`!`) view, reusing the tree's filter.

docs/actions.md

@@ -0,0 +1,262 @@
+# Actions (draft)
+
+**Status: draft, not implemented.** The spec for the first two write actions.
+Open questions are listed [at the end](#open-questions). Once they are
+answered, the decisions go into [decisions.md](decisions.md), and
+[requirements.md](requirements.md) and [ux-guide.md](ux-guide.md) are
+updated.
+
+## Principle
+
+Offer as few actions as possible, but enough to work with submodules.
+submarine shows what differs from what git records. The actions resolve such
+a difference in one of two directions:
+
+| Action | Direction | Key (proposed) |
+|---|---|---|
+| [Restore](#restore) | The worktree follows the recorded state | `u` |
+| [Stage pin](#stage-pin) | The recorded state follows the worktree | `s` |
+
+There is nothing else for now. Committing, pushing, switching branches and
+bumping a pin to the tip are done outside submarine. A bump is "check out
+the tip in the submodule, then `s`".
+
+## Restore
+
+Makes the selected repository, and everything below it, exactly what git
+records. It works on any submodule and on the superproject (header
+selected). Restoring the superproject gives the exact project that the
+current root commit specifies.
+
+### Target
+
+| Selected | Target commit | Branch |
+|---|---|---|
+| Superproject | `HEAD` | stays on the current branch |
+| Submodule | The pin in the parent's **index** (what the UI shows as *Pinned*) | see [Branches](#branches) |
+| Nested submodule, during the recursion | The gitlink in the restored parent's commit | as for a submodule |
+
+Restoring the superproject resets its index too, so **staged pins are
+discarded**: afterwards every pin is the one in `HEAD`. Restoring a submodule
+does not touch the parent's index, so a staged pin of that submodule stays
+and is the target. (See open question 2.)
+
+### Postconditions
+
+After a successful restore of repository R with target T:
+
+1. **R's HEAD is T.** The index and the worktree equal T's tree. No
+   modified, added, removed or conflicted files remain.
+2. **No in-progress operation** remains in R: merge, rebase, cherry-pick,
+   revert.
+3. **No untracked files or directories** remain in R. This includes leftover
+   directories of submodules that T no longer has (*untracked repository*).
+   Ignored files are kept (see open question 1).
+4. **Every submodule that T records is present and initialized**, even if
+   it was never initialized, is inactive (`submodule.<name>.active`) or has
+   `update = none / merge / rebase` configured. Its URL comes from T's
+   `.gitmodules` (synced into the config).
+5. **Each of those submodules is restored the same way**, with its gitlink
+   in T as its target, recursively at any depth.
+
+So the subtree shows `in sync` everywhere, except for states restore does
+not change: `unpushed`, behind/ahead of the ref, and `detached HEAD on pin`.
+
+The recursion follows **T**, not the tree loaded in the UI. A submodule that
+is only in T (for example, after switching branches) is initialized. A
+submodule that is only on disk is deleted as an untracked directory.
+
+### Branches
+
+- **Superproject:** stays on its branch. The branch is not moved, since the
+  target is its own `HEAD`.
+- **Submodule on the pin:** if HEAD is a branch that points at the target,
+  the branch stays checked out.
+- **Submodule off the pin:** HEAD is detached at the target. The branch that
+  was checked out is **not moved**, so its commits stay on it.
+
+Restore never moves, creates or deletes a branch.
+
+### What can be lost
+
+Restore discards work. The things it can lose:
+
+| Lost | Where it comes from |
+|---|---|
+| Changed files | modified, added, removed, renamed files (`changed`) |
+| Untracked files | `changed` (untracked) |
+| Conflicts and in-progress operations | `conflict`; merge, rebase, cherry-pick, revert state |
+| Commits | A detached HEAD off the pin whose commits are on no branch, tag or remote ref (only the reflog still has them) |
+| Repositories | An untracked directory that is a repository with its **own** `.git` directory (a clone that was never added as a submodule). Its commits may exist nowhere else. A removed submodule whose git directory is absorbed into `.git/modules` loses only its worktree. Its objects stay |
+
+Nothing else is lost. Branches, stashes, remote refs, ignored files and
+absorbed submodule git directories stay.
+
+### Confirmation
+
+- **Nothing would be lost** (only `off pin`, `missing`, a staged pin of the
+  root): restore runs at once, without a question.
+- **Something would be lost:** a confirmation line opens above the footer,
+  like the filter line. It says what is discarded, summed over the subtree:
+
+  ```
+  Restore src/app? Discards 7 changed files in 3 submodules, 2 detached commits, 1 repository.   y restore · n cancel
+  ```
+
+  `y` runs it. `n`, `esc` or any other key cancels.
+- **The state is not fully known** (a status in the subtree is still
+  loading or failed to load): the line says so (`… · 2 submodules not
+  loaded`) and needs the same `y`. Restore does not wait for the loading.
+- Lost repositories and commits are shown in the Danger color, files in
+  Warn.
+
+The summary only covers the submodules that are loaded. Children of a
+submodule that is not initialized are unknown. They are created fresh, so
+nothing of them can be lost.
+
+### Network
+
+A restore may need objects that are not on disk:
+
+- a submodule that was never cloned (`not initialized`, no git directory in
+  `.git/modules`);
+- a target commit that was never fetched.
+
+Proposal: **restore may clone and fetch, but only for objects that are
+missing**, and never prompts (`GIT_TERMINAL_PROMPT=0`, as for `Fetch`).
+This changes the rule "the provider uses the network only in `Fetch`"
+(AGENTS.md, N8). The alternative is to fail with "pinned commit … not
+fetched" and leave cloning to the user (open question 3).
+
+### Running, progress and errors
+
+- The selected row (or the header) shows a spinner and `restoring` in the
+  status column until the restore ends. The header shows `restoring src/app`
+  where the fetch progress usually is.
+- Only one write action runs at a time. Pressing `u` or `s` meanwhile
+  flashes `wait for the restore of src/app to finish`. Navigation and
+  everything else keep working.
+- A running background fetch does not block a restore.
+- Done: flash `restored src/app`. The watcher refreshes the affected rows.
+  The app also reloads the subtree, because the structure can have changed.
+- Failure: the restore stops at the first repository that fails. The footer
+  flashes `restore failed in src/app/lib: <git's message>`, and the detail
+  pane of the selected node shows the same message until the next restore.
+  Restore is idempotent, so it can be run again after fixing the cause.
+
+### Implementation note
+
+For each repository, top-down (`T` = target):
+
+```sh
+git merge --abort / rebase --abort / cherry-pick --abort / revert --abort   # whichever is in progress
+git checkout --detach --force T      # submodule off the pin; superproject: git reset --hard HEAD
+git reset --hard T
+git clean -ffd                       # -ff: also untracked nested repositories
+git submodule sync
+git submodule init                   # all submodules of T, including inactive ones
+# for each gitlink in T: make sure the repo exists (clone/absorb), then recurse
+```
+
+The repository can be walked by submarine itself, not by `git submodule
+update --recursive`, so progress, the loss check and errors are per
+repository. `git submodule update --init --checkout --force` is an option for
+the clone step. The loss check runs right before the restore, against the
+current state, not the displayed one.
+
+## Stage pin
+
+Records the commit checked out in a submodule as its new pin in the
+parent's index. It is the same as `git add <path>` in the parent, but only
+when it is safe.
+
+### Available when
+
+All of:
+
+- the selected node is a submodule, not the superproject;
+- it is `off pin` (`Checkout == CheckoutDiffers`): HEAD differs from the
+  pin in the parent's index;
+- its worktree is **clean** (`Worktree == WorktreeClean`). Uncommitted
+  changes, untracked files and conflicts count as dirty, the same rule as
+  the `changed` issue. A moved nested pin counts as a change too, so nested
+  submodules are staged bottom-up: first inside the submodule, then the
+  submodule itself (after a commit in it, outside submarine).
+
+Changes *inside* nested submodules don't count. Like the `changed` issue,
+staging only looks at the submodule's own worktree.
+
+### Effect
+
+- The parent's index records the submodule's HEAD as the gitlink of its
+  path. Nothing else changes: no worktree, no other index entry, no commit.
+- The submodule then shows `staged` (or `●` next to an issue), and the
+  `off pin` issue is gone.
+- If the checkout equals the pin in the parent's `HEAD`, staging removes
+  the staged pin instead (the index equals `HEAD` again).
+- If the checked-out commit is not pushed, it is staged anyway. The row
+  then shows `unpushed` (Danger), which is the warning.
+- There is no confirmation: nothing is lost.
+- Undo: there is no unstage action. `git restore --staged <path>` in the
+  parent undoes it. Restoring the superproject also discards every staged
+  pin, together with everything else.
+
+### Implementation note
+
+```sh
+# in the submodule
+git rev-parse HEAD                  # must still be the SHA shown in the UI, else abort
+# in the parent
+git update-index --cacheinfo 160000,<sha>,<path>
+```
+
+`update-index` stages exactly the SHA that was checked, independent of the
+worktree. Flash: `staged pin of src/app` on success; git's message on
+failure.
+
+## Keys and palette
+
+Both are submodule keys (`keyMap.Submodule`), shown in the detail pane's
+palette, or in the footer, **only while they apply** to the selection:
+
+| Key | Shown when | Pressed when not applicable (flash) |
+|---|---|---|
+| `u` restore | The node or a loaded descendant has an issue restore fixes (`changed`, `conflict`, `missing`, `off pin`), or the root has a staged pin | `nothing to restore in src/app` |
+| `s` stage pin | [Available](#available-when) | `src/app is on its pin` / `src/app has uncommitted changes; commit or restore them first` / `the superproject has no pin` |
+
+Full help (`?`) always lists both.
+
+## Testing
+
+- Provider: tests on fixtures from `scripts/make-fixture.sh`, which builds
+  every state. For restore: changed, untracked, untracked repository
+  (absorbed and standalone), conflict, rebase in progress, off pin on a
+  branch, off pin detached with unreachable commits, not initialized,
+  inactive, `update = none`, a submodule added and one removed between two
+  root commits, nested at depth ≥ 2. Assert the postconditions with
+  `git status --porcelain --ignored=no` and `git submodule status
+  --recursive`, and that branches are unchanged. For stage pin: index entry,
+  refusal on a dirty worktree, refusal when HEAD moved.
+- Loss summary: unit tests on `submodule` (no UI), like `Status.Issues()`.
+- UI: run it on a fixture in tmux (see
+  [architecture.md](architecture.md#testing)). Check the confirmation line,
+  the spinner, the flash messages and the palette.
+
+## Open questions
+
+1. **Ignored files.** Should restore also delete ignored files (`git clean
+   -x`)? That is the literal "no additional files", but it deletes `.env`,
+   `node_modules`, build output and IDE settings in every submodule.
+   *Proposal: keep ignored files.*
+2. **Target of a submodule restore with a staged pin.** The staged pin
+   (index, what the UI shows as *Pinned*, what `git submodule update` does)
+   or the committed one (parent's `HEAD`, which also unstages)?
+   *Proposal: the index. Unstaging happens only through a superproject
+   restore.*
+3. **Network.** May restore clone uninitialized submodules and fetch missing
+   pins (non-interactive), or should it fail and ask for `f` / a manual
+   clone? *Proposal: allow it, only for missing objects.*
+4. **Keys.** `u` restore, `s` stage pin? `R` would sit next to `r` reload,
+   which is a dangerous mix-up for a destructive action.
+5. **Confirmation without loss.** Is "no question when nothing is lost" OK,
+   or should restore always ask?

docs/decisions.md

@@ -282,3 +282,17 @@ problem is visible while a submodule is selected.
   Without an upstream the usual resolution applies.
 - The root is not in `Walk`, so counts, fetch and loading logic stay
   submodule-only; the app tracks it by the path `""`.
+
+## Problems only reuses the filter's tree reduction
+
+`!` shows only submodules with issues. Instead of a second view, the tree's
+filter got a second criterion: a submodule matches if its path contains the
+term *and*, with problems only, it has an issue. Ancestors of matches stay as
+context, expanded, so a danger deep in the tree is reachable without
+unfolding anything. Unlike the filter text it is a mode that outlives the
+filter line, so it has its own notice line above the footer: a short list
+must not look like a healthy repository (D4). Loading and failed submodules
+count as problems because their state is unknown (D7 counts `error` as danger
+too); the cost is that rows vanish as statuses arrive, so the selection is
+refitted after each status. Staged pins are not shown by it, since they are
+not issues.

docs/requirements.md

@@ -120,13 +120,21 @@ commit hashes. It doesn't answer the questions users actually have:
   submodule (none if nothing matches); closing the filter keeps the
   selection (the superproject if none is left). See [Filter](ux-guide.md#filter).
 
+- **F55** `!` toggles "problems only": the tree shows only submodules with
+  an issue (**F10**) or an unknown state (loading, `error`), plus their
+  ancestors, expanded. It combines with the filter (**F54**) and stays when
+  the filter closes. A line above the footer says `problems only`, so a short
+  list is not mistaken for a healthy repository. See
+  [Problems only](ux-guide.md#problems-only).
+
 ### Actions (planned, not implemented)
 
 | Key | Action |
 |---|---|
 | `u` | Check out the pinned commit (`git submodule update`) |
 | `b` | Bump the pin to the tip of its ref |
-| `!` | Show only submodules with issues |
+
+See [actions.md](actions.md) for the draft of the write actions.
 
 ## Usage
 

docs/ux-guide.md

@@ -220,7 +220,8 @@ colors in components.
 | `r` | Reload everything (e.g. after editing files) |
 | `c` | Copy the absolute directory of the selected submodule to the clipboard (OSC 52, so it also works over SSH; needs terminal support, in tmux `set -g set-clipboard on`). The footer confirms with `copied <path>`. Without a local provider (mock) the path relative to the superproject is copied |
 | `/` | Open the filter, see [Filter](#filter) |
-| `u`, `b`, `!` | Planned actions (see requirements) |
+| `!` | Toggle problems only, see [Problems only](#problems-only) |
+| `u`, `b` | Planned actions (see requirements) |
 
 "First child" always means the first child **as displayed** (children are
 grouped by directory).
@@ -250,6 +251,29 @@ match vanish. If nothing matches the tree says `no submodule matches`.
 - The filter line shows the keys that apply on its right.
 - The header counts are not filtered.
 
+### Problems only
+
+`!` reduces the tree to what needs attention. It uses the filter's rules
+(matches with their ancestors, shown expanded, see [Filter](#filter)), with
+"match" meaning *has an issue* (`Status.Issues()`) instead of *path contains
+the term*.
+
+- A submodule that is still loading or failed to load (`error`) counts as a
+  problem, since its state is unknown (as in the hidden counts, D7). Healthy
+  submodules vanish when their status arrives.
+- A staged pin is not an issue and does not show the row.
+- It combines with the filter (both must match). Unlike the filter it is a
+  mode, not an input: it stays until `!` is pressed again, also after `esc`
+  closed the filter.
+- A line above the footer shows `problems only` (yellow) and `! show all`.
+  While the filter line is open, its hint starts with `problems only (!)`
+  instead.
+- With no problem the tree says `no problems`.
+- The selection follows the filter's rule: if it stops being visible (also
+  when a status changes), the next visible submodule is selected, else the
+  previous one. The superproject stays selectable.
+- The header counts are not filtered.
+
 ### Key reference
 
 Every key in the UI, where it is shown, and whether it works. Update this
@@ -272,7 +296,7 @@ where the palette can't be shown, see [Key bar and palette](#key-bar-and-palette
 | `f` | Fetch all repositories | Global | Help | yes |
 | `r` | Reload everything | Global | Help | yes |
 | `/` | Filter | Global | Help | yes |
-| `!` | Problems only | Global | Help | no (flashes "not implemented") |
+| `!` | Problems only (toggle) | Global | Help | yes |
 | `?` | Toggle full help | Global | Bar, Help | yes |
 | `q`, `ctrl+c` | Quit | Global | Bar, Help | yes |
 

internal/tui/app.go

@@ -199,6 +199,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			} else {
 				s.Status, s.Err = msg.status, nil
 			}
+			m.tree.Refit()
 		}
 		if m.loads.done(msg.path) {
 			return m, m.loadStatus(msg.path)
@@ -386,7 +387,10 @@ func (m Model) handleKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		m.filtering = true
 		m.layout()
 		return m, m.filter.Focus()
-	case key.Matches(msg, k.Update, k.Bump, k.Issues):
+	case key.Matches(msg, k.Issues):
+		m.tree.SetProblemsOnly(!m.tree.ProblemsOnly())
+		m.layout()
+	case key.Matches(msg, k.Update, k.Bump):
 		cmd := m.footer.Flash("“" + msg.String() + "” is not implemented in the prototype")
 		m.layout()
 		return m, cmd
@@ -438,6 +442,9 @@ func (m Model) filterView() string {
 	if !m.filter.Focused() {
 		hint = "/ edit • esc close"
 	}
+	if m.tree.ProblemsOnly() {
+		hint = "problems only (!) • " + hint
+	}
 	hint = theme.Fg(m.theme.Muted).Render(hint)
 	m.filter.Width = max(m.width-lipgloss.Width(hint)-6, 1)
 	in := m.filter.View()
@@ -445,6 +452,19 @@ func (m Model) filterView() string {
 	return lipgloss.NewStyle().Width(m.width).Padding(0, 1).Render(in + strings.Repeat(" ", gap) + hint)
 }
 
+// extraLine reports whether a line above the footer is shown: the filter, or
+// the notice that only problems are shown.
+func (m Model) extraLine() bool { return m.filtering || m.tree.ProblemsOnly() }
+
+// problemsView is the line above the footer while only problems are shown, so
+// a short list is not mistaken for a healthy repository.
+func (m Model) problemsView() string {
+	left := theme.Fg(m.theme.Warn).Render("problems only")
+	right := theme.Fg(m.theme.Muted).Render("! show all")
+	gap := max(m.width-2-lipgloss.Width(left)-lipgloss.Width(right), 1)
+	return lipgloss.NewStyle().Width(m.width).Padding(0, 1).Render(left + strings.Repeat(" ", gap) + right)
+}
+
 // copyPath copies the absolute directory of the selected submodule to the
 // clipboard, or its path in the superproject if the provider can't tell.
 func (m Model) copyPath() (tea.Model, tea.Cmd) {
@@ -470,7 +490,7 @@ func (m Model) copyPath() (tea.Model, tea.Cmd) {
 func (m *Model) layout() {
 	m.footer.SetWidth(m.width)
 	bodyHeight := m.height - headerHeight - lipgloss.Height(m.footer.View())
-	if m.filtering {
+	if m.extraLine() {
 		bodyHeight--
 	}
 	bodyHeight = max(bodyHeight, 0)
@@ -508,6 +528,8 @@ func (m Model) View() string {
 	parts := []string{zone.Mark(m.tree.RootZone(), head), body}
 	if m.filtering {
 		parts = append(parts, m.filterView())
+	} else if m.tree.ProblemsOnly() {
+		parts = append(parts, m.problemsView())
 	}
 	return zone.Scan(lipgloss.JoinVertical(lipgloss.Left, append(parts, m.footer.View())...))
 }

internal/tui/tree/filter.go

@@ -8,7 +8,7 @@ import (
 
 // SetFilter shows only the submodules whose path contains term (ignoring
 // case), plus their ancestors, which are shown expanded. An empty term
-// removes the filter.
+// removes the filter. It combines with SetProblemsOnly.
 //
 // If the selected submodule is filtered out, the next visible one is
 // selected (the previous one if there is none after it, none if nothing
@@ -21,15 +21,46 @@ func (m *Model) SetFilter(term string) {
 	}
 	old := m.cursor
 	m.filter = term
-	if term == "" {
+	m.narrow(old)
+}
+
+// SetProblemsOnly shows only the submodules with issues, plus their
+// ancestors, which are shown expanded. A submodule whose status is loading or
+// failed to load counts as a problem, since its state is unknown. The
+// selection behaves as with SetFilter.
+func (m *Model) SetProblemsOnly(on bool) {
+	if on == m.problemsOnly {
+		return
+	}
+	old := m.cursor
+	m.problemsOnly = on
+	m.narrow(old)
+}
+
+// ProblemsOnly reports whether only submodules with issues are shown.
+func (m Model) ProblemsOnly() bool { return m.problemsOnly }
+
+// Refit keeps the selection visible after statuses changed, which can make a
+// submodule enter or leave the problems-only view.
+func (m *Model) Refit() {
+	if m.problemsOnly {
+		m.reselect(m.cursor)
+		m.clampOffset()
+	}
+}
+
+// narrow fixes the selection after the filter or the problems-only view
+// changed.
+func (m *Model) narrow(old *submodule.Submodule) {
+	if m.narrowed() {
+		m.reselect(old)
+	} else {
 		for p := parentOf(old); p != nil; p = p.Parent {
 			m.expanded[p.Path] = true
 		}
 		if m.cursor == nil {
 			m.cursor = m.firstNode()
 		}
-	} else {
-		m.reselect(old)
 	}
 	m.clampOffset()
 }
@@ -37,6 +68,9 @@ func (m *Model) SetFilter(term string) {
 // Filter returns the active filter term in lower case.
 func (m Model) Filter() string { return m.filter }
 
+// narrowed reports whether the tree is reduced to matches.
+func (m Model) narrowed() bool { return m.filter != "" || m.problemsOnly }
+
 func parentOf(s *submodule.Submodule) *submodule.Submodule {
 	if s == nil {
 		return nil
@@ -106,10 +140,10 @@ func (m *Model) appendAll(out *[]row, mods []*submodule.Submodule, depth int) {
 	}
 }
 
-// isExpanded reports whether the children of s are shown. While filtering,
+// isExpanded reports whether the children of s are shown. While narrowed,
 // that is the case if a match is below s, whatever the user expanded.
 func (m *Model) isExpanded(s *submodule.Submodule) bool {
-	if m.filter == "" {
+	if !m.narrowed() {
 		return m.expanded[s.Path]
 	}
 	for _, c := range s.Children {
@@ -122,7 +156,7 @@ func (m *Model) isExpanded(s *submodule.Submodule) bool {
 
 // filtered returns the submodules of mods that pass the filter.
 func (m *Model) filtered(mods []*submodule.Submodule) []*submodule.Submodule {
-	if m.filter == "" {
+	if !m.narrowed() {
 		return mods
 	}
 	var out []*submodule.Submodule
@@ -136,7 +170,7 @@ func (m *Model) filtered(mods []*submodule.Submodule) []*submodule.Submodule {
 
 // shown reports whether s matches the filter or has a descendant that does.
 func (m *Model) shown(s *submodule.Submodule) bool {
-	if strings.Contains(strings.ToLower(s.Path), m.filter) {
+	if strings.Contains(strings.ToLower(s.Path), m.filter) && (!m.problemsOnly || hasProblem(s)) {
 		return true
 	}
 	for _, c := range s.Children {
@@ -146,3 +180,9 @@ func (m *Model) shown(s *submodule.Submodule) bool {
 	}
 	return false
 }
+
+// hasProblem reports whether s has an issue or an unknown state (loading, or
+// failed to load, like HiddenIn counts it).
+func hasProblem(s *submodule.Submodule) bool {
+	return s.Status == nil || len(s.Status.Issues()) > 0
+}

internal/tui/tree/tree.go

@@ -27,11 +27,13 @@ type Model struct {
 	roots    []*submodule.Submodule
 	expanded map[string]bool // keyed by Submodule.Path; kept when ancestors collapse
 	filter   string          // lower-case; empty if not filtering
-	cursor   *submodule.Submodule
-	offset   int // index of the first visible row
-	width    int
-	height   int
-	spinner  string
+	// problemsOnly hides submodules without issues; it combines with filter.
+	problemsOnly bool
+	cursor       *submodule.Submodule
+	offset       int // index of the first visible row
+	width        int
+	height       int
+	spinner      string
 }
 
 func New(t theme.Theme) Model {
@@ -365,8 +367,12 @@ func (m Model) View() string {
 			lines = append(lines, m.nodeLine(r, nameColW, refW))
 		}
 	}
-	if len(rows) == 0 && m.filter != "" {
-		lines = append(lines, theme.Fg(m.theme.Muted).Width(m.width).Render(" no submodule matches"))
+	if len(rows) == 0 && m.narrowed() {
+		none := " no submodule matches"
+		if m.filter == "" {
+			none = " no problems"
+		}
+		lines = append(lines, theme.Fg(m.theme.Muted).Width(m.width).Render(none))
 	}
 	for len(lines) < m.height {
 		lines = append(lines, strings.Repeat(" ", m.width))

internal/tui/tree/tree_test.go

@@ -411,3 +411,83 @@ func TestFilterKeepsRoot(t *testing.T) {
 		t.Error("closing the filter should keep the root")
 	}
 }
+
+// healthy gives every submodule of the fixture an issue-free status, then
+// marks the given paths as changed.
+func healthy(t *testing.T, m *Model, changed ...string) {
+	t.Helper()
+	submodule.Walk(m.roots, func(s *submodule.Submodule) {
+		s.Status = &submodule.Status{Pin: submodule.PinInfo{Pushed: true}}
+		for _, p := range changed {
+			if s.Path == p {
+				s.Status.Worktree = submodule.WorktreeModified
+			}
+		}
+	})
+}
+
+func TestProblemsOnlyShowsIssuesWithAncestors(t *testing.T) {
+	m := newTree(t)
+	healthy(t, m, "d")
+	m.SetProblemsOnly(true)
+	want := []string{"src/", "b", "modules/", "c", "d"}
+	if got := visible(m); !equal(got, want) {
+		t.Fatalf("rows = %v, want %v", got, want)
+	}
+	assertCursor(t, m, "b") // a was selected and is healthy: next available
+	m.Select("d")
+	m.SetProblemsOnly(false)
+	assertCursor(t, m, "d")
+	if got := visible(m); len(got) != 8 {
+		t.Fatalf("rows = %v, want all expanded to d", got)
+	}
+}
+
+func TestProblemsOnlyKeepsUnknownStates(t *testing.T) {
+	m := newTree(t)
+	healthy(t, m)
+	f := m.roots[2]
+	f.Status, f.Err = nil, os.ErrNotExist // failed to load
+	m.roots[0].Status = nil               // still loading
+	m.SetProblemsOnly(true)
+	if got, want := visible(m), []string{"a", "src/", "f"}; !equal(got, want) {
+		t.Fatalf("rows = %v, want %v", got, want)
+	}
+}
+
+func TestProblemsOnlyWithoutProblemsKeepsRoot(t *testing.T) {
+	m := New(theme.Default())
+	m.SetRoot(&submodule.Submodule{Status: &submodule.Status{Root: true}})
+	m.SetRoots(fixture())
+	m.SetSize(80, 20)
+	healthy(t, &m)
+	m.SetProblemsOnly(true)
+	if len(m.rows()) != 0 || !m.RootSelected() {
+		t.Fatalf("rows %v, root selected %v", visible(&m), m.RootSelected())
+	}
+	m.Down() // must not panic
+}
+
+func TestProblemsOnlyCombinesWithFilter(t *testing.T) {
+	m := newTree(t)
+	healthy(t, m, "d", "f")
+	m.SetProblemsOnly(true)
+	m.SetFilter("f")
+	if got, want := visible(m), []string{"src/", "f"}; !equal(got, want) {
+		t.Fatalf("rows = %v, want %v", got, want)
+	}
+	m.SetFilter("")
+	if !m.ProblemsOnly() || len(visible(m)) != 6 {
+		t.Fatalf("closing the filter keeps problems only: %v", visible(m))
+	}
+}
+
+func TestRefitMovesSelectionWhenProblemDisappears(t *testing.T) {
+	m := newTree(t)
+	healthy(t, m, "a", "f")
+	m.SetProblemsOnly(true)
+	assertCursor(t, m, "a")
+	m.roots[0].Status.Worktree = submodule.WorktreeClean
+	m.Refit()
+	assertCursor(t, m, "f")
+}