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+# Excluding a value from a search
+
+Resolves backlog item **86**. Follows item 85, which shipped the two operations
+this adds a third to. Depends on nothing unshipped.
+
+## What this is
+
+Every right-click search menu gains a third entry, **Exclude from search**,
+which narrows the current query by everything that is *not* the value under the
+cursor. The two shipped entries keep their labels and their behaviour.
+
+The user's words, from the notes on 2026-08-14: "the current available search
+options are to run the query from scratch or add to the existing query. A
+missing option is to add negatively (not)."
+
+## Why it is not a one-line menu addition
+
+Item 85 shipped exactly two operations and encoded the choice between them as a
+single `bool extend`, carried end to end. `MessageView::addSearchEntries`
+(`src/messageview.cpp:566`) builds the pair per offer,
+`MessageDetailsDialog` (`src/messagedetailsdialog.cpp:88`) repeats it per row,
+and `MainWindow::runSearchFromPane` (`src/mainwindow.cpp:1654`) branches on it:
+
+```cpp
+extend ? SearchTerm::extend(m_queryEdit->text(), query) : query;
+```
+
+`SearchTerm` has no exclusion form at all. So there is no third state for a new
+menu entry to select, and the signature cannot express one. The work is a
+widening of that signature plus one function, not a menu edit.
+
+## The grammar
+
+One function in `src/searchterm.h`, beside `extend()`:
+
+```cpp
+QString exclude(const QString &existing, const QString &addition);
+```
+
+It returns `(existing) AND NOT (addition)`.
+
+**Both sides are parenthesised, and that is load-bearing rather than tidy.**
+The query bar may hold a hand-written disjunction. Unparenthesised,
+`a or b AND NOT c` binds as `a or (b AND NOT c)`: the exclusion covers only the
+second term, and every message matching `a` stays on screen including the ones
+the user asked to be rid of. Nothing reports an error. This is the same trap
+`extend()` documents and the same one the `post-new` hook handles when it scopes
+a rule with `tag:new`.
+
+### The empty cases, and where they differ from `extend()`
+
+| `existing` | `addition` | result |
+|---|---|---|
+| non-empty | non-empty | `(existing) AND NOT (addition)` |
+| non-empty | empty | `existing`, untouched |
+| empty | non-empty | **empty string** |
+| empty | empty | empty string |
+
+The third row is the decision. `extend()` returns the addition alone when
+`existing` is empty, because narrowing nothing by `x` sensibly means `x`.
+Excluding from nothing would mean `NOT (addition)`: the entire Maildir minus
+one sender. That is a legitimate query and an implausible thing to have meant by
+right-clicking a value in a fresh window, so the grammar refuses to build it.
+
+The UI never asks for it either (see the guard below). Two layers, deliberately:
+the guard is what the user sees, and the empty return is what stops a future
+caller that forgets the guard from producing a whole-Maildir scan.
+
+## The signal
+
+`bool extend` cannot carry three states. It becomes an enum in
+`src/searchterm.h`, beside the functions it selects between:
+
+```cpp
+enum class SearchMode { Replace, Narrow, Exclude };
+```
+
+It crosses **no thread boundary**, so the `Q_ENUM` metatype trap recorded in
+`CLAUDE.md` does not apply here. Every one of these connections is direct; that
+trap belongs to the queued signals into `NotmuchWorker`.
+
+Four signatures change:
+
+| where | from | to |
+|---|---|---|
+| `MessageView::searchRequested` | `(QString, bool)` | `(QString, SearchMode)` |
+| `MessageDetailsDialog::searchRequested` | `(QString, bool)` | `(QString, SearchMode)` |
+| `MessageDetailsDialog::requestSearch` | `(HeaderRow, bool)` | `(HeaderRow, SearchMode)` |
+| `MainWindow::runSearchFromPane` | `(QString, bool)` | `(QString, SearchMode)` |
+
+`runSearchFromPane` becomes a three-way switch over the mode. Its existing
+comment stays true and stays put: the result goes through the query bar and
+`runCurrentQuery()`, so the account scope, the generation counter and the
+flat-mode reset behave exactly as they do for a typed query. Nothing here builds
+a second query path.
+
+## The guard
+
+The menus cannot currently tell whether the query bar is empty. `MessageView`
+and `MessageDetailsDialog` both emit outward and never read the query, and the
+dialog is a child of the view rather than of the window.
+
+`MainWindow` pushes the fact down:
+
+```cpp
+void MessageView::setHasQuery(bool hasQuery);
+```
+
+`MainWindow` already hangs a lambda on `m_queryEdit`'s `textChanged` at
+`src/mainwindow.cpp:373`, for the Save button's enabled state. That lambda gains
+one line. `MessageView` stores the bool and passes it to
+`MessageDetailsDialog` at construction, since the dialog is built fresh per
+invocation and cannot go stale.
+
+Both menu builders then disable the Exclude action when the bool is false. The
+entry stays **visible and greyed**, not hidden: a user exploring a fresh window
+is exactly the one who should be able to see that the feature exists.
+
+Rejected alternatives, recorded so they are not revisited. A `std::function`
+callback into `MainWindow` is always fresh but adds an indirection with one
+implementation and a dangling-callback risk. Leaving the entry always enabled
+and having `MainWindow` silently do nothing is fewer lines and worse: a live
+menu entry that does nothing is a worse failure than a greyed one.
+
+## The menus
+
+Three entries, in this order, in both surfaces:
+
+```
+Search for this
+Add to search
+Exclude from search
+```
+
+The two shipped labels are untouched, so nothing the user already knows moves.
+All three are wrapped in `tr()`.
+
+Both call sites: `MessageView::addSearchEntries` (`src/messageview.cpp:566`),
+which builds a submenu per offer, and the per-row lambda in
+`MessageDetailsDialog` (`src/messagedetailsdialog.cpp:88`).
+
+## Testing
+
+**`test_searchterm`** carries the grammar, and needs no widget, no painter and
+no web engine. Cover every row of the empty-case table, and cover the
+disjunction: `exclude("tag:inbox or tag:flagged", "from:\"x\"")` must
+parenthesise the left side, which is the assertion that fails if someone
+"simplifies" the parentheses away.
+
+**Assert on the constructed string, never on a result count.** notmuch rejects
+almost nothing: `from:((((` parses cleanly and matches zero, so a malformed
+query produces an empty result rather than an error. A test asserting a failure
+or a `-1` count passes against correct code and against broken code alike. This
+is recorded in `searchterm.h` and in `test_notmuchworker.cpp`, and has been
+learned twice already.
+
+**`test_messagedetailsdialog`** covers the guard: the Exclude action is disabled
+when the dialog is constructed with no query and enabled when it is constructed
+with one.
+
+**The dialog inherits item 85's ordering trap.** A modal's signal to its parent
+is a DIRECT connection, so the emit runs the handler synchronously while
+`exec()` is still on the stack. `accept()` must run before the emit, or the
+search clears the model and blanks the pane behind a dialog the user still has
+to dismiss, while it holds the `m_items` it was built from. The new action is on
+the same path and has the same requirement.
+
+**Its mutation check hangs rather than fails.** Without the `accept()`, nothing
+ever leaves `exec()`. A hung `test_messagedetailsdialog` binary also leaves a
+stale binary that a later `ctest` will re-run, which is item 84's second trap:
+the failure appears to persist after being fixed. Kill the binary and rebuild
+before concluding anything about a hang here.
+
+## Out of scope
+
+The thread list's context menu. Item 85 left it alone deliberately and that
+holds: `ThreadSummary::authors` comes from `notmuch_thread_get_authors` and is a
+display summary reading like "Alice, Bob", so a `from:` query built from it
+matches nothing. Item 78 carries what is left of that.
+
+## Size
+
+**S.** The grammar is one function beside an existing one with an existing test
+binary. The spread is the signature change across three files.