Thread context.Context through blocking I/O entry points

Accept ctx as the first parameter on the blocking I/O entry points and
propagate it to downstream blocking calls so the work is cancellable from
the process entry point:

- appconfig.Load / LoadWithOptions: honor ctx before the blocking file
  reads, returning defaults on a cancelled context.
- LSP: lsp.Server.Run(ctx) ties the serve loop to the caller context via a
  new watchParentContext bridge (cancels the server context, aborting
  in-flight LLM work). Threaded through hexailsp.Run/RunWithConfig/
  RunWithFactory and runtimeconfig.Store.Reload.
- MCP: mcp.Server.Run(ctx) stops accepting requests once ctx is cancelled;
  threaded through hexaimcp.Run/RunWithFactory/RunBackfill.
- editor: RunEditor/OpenTempAndEdit/OpenFile take ctx and use
  exec.CommandContext so a cancelled context kills the editor subprocess;
  threaded through hexaicli, hexaiaction and askcli call sites.

Top-level callers (cmd/hexai-lsp-server, cmd/hexai-mcp-server) now build a
signal-cancelled context (SIGINT/SIGTERM) so shutdown tears the run down
cleanly. Updated comments to explain the cancellation flow and added
cancellation tests for the LSP/MCP loops, editor, and config load.

All tests pass with -race; cross-package coverage 86.2%.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

2 files changed, 8 insertions, 7 deletions

diff --git a/internal/askcli/command_edit.go b/internal/askcli/command_edit.go
index 27c9106..a82d575 100644
--- a/internal/askcli/command_edit.go
+++ b/internal/askcli/command_edit.go
@@ -10,9 +10,10 @@ import (
 
 // captureFromEditor opens the user's editor on a temporary file pre-filled with
 // the given initial content and returns its trimmed contents after the editor
-// exits. It is a variable so tests can stub it.
-var captureFromEditor = func(initial []byte) (string, error) {
-	return editor.OpenTempAndEdit(initial)
+// exits. ctx is forwarded to the editor subprocess so it can be cancelled with
+// the surrounding command. It is a variable so tests can stub it.
+var captureFromEditor = func(ctx context.Context, initial []byte) (string, error) {
+	return editor.OpenTempAndEdit(ctx, initial)
 }
 
 // handleEdit opens the configured editor on a temporary file. With no selector
@@ -22,7 +23,7 @@ func (d *Dispatcher) handleEdit(ctx context.Context, args []string, stdout, stde
 	if len(args) >= 2 {
 		return d.editTaskDescription(ctx, args[1], stdout, stderr)
 	}
-	description, err := captureFromEditor(nil)
+	description, err := captureFromEditor(ctx, nil)
 	if err != nil {
 		writeInfoError(stderr, err)
 		return 1, nil
@@ -43,7 +44,7 @@ func (d *Dispatcher) editTaskDescription(ctx context.Context, selector string, s
 		return code, nil
 	}
 
-	description, err := captureFromEditor([]byte(tasks[0].Description))
+	description, err := captureFromEditor(ctx, []byte(tasks[0].Description))
 	if err != nil {
 		writeInfoError(stderr, err)
 		return 1, nil
diff --git a/internal/askcli/command_edit_test.go b/internal/askcli/command_edit_test.go
index 80cbd56..4db19c1 100644
--- a/internal/askcli/command_edit_test.go
+++ b/internal/askcli/command_edit_test.go
@@ -12,7 +12,7 @@ import (
 func stubEditorCapture(t *testing.T, content string, err error) {
 	t.Helper()
 	old := captureFromEditor
-	captureFromEditor = func(initial []byte) (string, error) {
+	captureFromEditor = func(_ context.Context, initial []byte) (string, error) {
 		return content, err
 	}
 	t.Cleanup(func() { captureFromEditor = old })
@@ -60,7 +60,7 @@ func TestHandleEdit_ExistingTaskModifiesDescription(t *testing.T) {
 
 	var initialContent []byte
 	old := captureFromEditor
-	captureFromEditor = func(initial []byte) (string, error) {
+	captureFromEditor = func(_ context.Context, initial []byte) (string, error) {
 		initialContent = initial
 		return "updated description", nil
 	}