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>

1 files changed, 3 insertions, 2 deletions

diff --git a/internal/appconfig/custom_validation_more_test.go b/internal/appconfig/custom_validation_more_test.go
index 36212aa..255963b 100644
--- a/internal/appconfig/custom_validation_more_test.go
+++ b/internal/appconfig/custom_validation_more_test.go
@@ -1,6 +1,7 @@
 package appconfig
 
 import (
+	"context"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -19,7 +20,7 @@ instruction = "x"
 id = "no-title"
 instruction = "x"
 `)
-	cfg := Load(newLogger())
+	cfg := Load(context.Background(), newLogger())
 	if err := cfg.Validate(); err == nil || (!strings.Contains(err.Error(), "missing required field id") && !strings.Contains(err.Error(), "missing required field title")) {
 		t.Fatalf("expected missing field error, got %v", err)
 	}
@@ -40,7 +41,7 @@ hotkey = "too"
 [tmux]
 custom_menu_hotkey = "ab"
 `)
-	cfg := Load(newLogger())
+	cfg := Load(context.Background(), newLogger())
 	if err := cfg.Validate(); err == nil || (!strings.Contains(err.Error(), "hotkey must be a single character") && !strings.Contains(err.Error(), "invalid tmux.custom_menu_hotkey")) {
 		t.Fatalf("expected invalid hotkey error, got %v", err)
 	}