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, 19 insertions, 2 deletions

diff --git a/internal/mcp/server_test.go b/internal/mcp/server_test.go
index 00a7823..8374a24 100644
--- a/internal/mcp/server_test.go
+++ b/internal/mcp/server_test.go
@@ -3,6 +3,7 @@ package mcp
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -397,12 +398,28 @@ func TestServer_Run(t *testing.T) {
 		logger := log.New(io.Discard, "", 0)
 		server := NewServer(inBuf, outBuf, logger, store, nil)
 
-		err := server.Run()
+		err := server.Run(context.Background())
 		if err != nil {
 			t.Errorf("Run() error = %v, want nil on EOF", err)
 		}
 	})
 
+	t.Run("exits on cancelled context", func(t *testing.T) {
+		store := &mockPromptStore{prompts: make(map[string]*promptstore.Prompt)}
+		// A pipe with no data would otherwise block in readMessage; an
+		// already-cancelled context makes Run return before reading.
+		pr, _ := io.Pipe()
+		outBuf := &bytes.Buffer{}
+		logger := log.New(io.Discard, "", 0)
+		server := NewServer(pr, outBuf, logger, store, nil)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+		if err := server.Run(ctx); err != nil {
+			t.Errorf("Run() error = %v, want nil on cancelled ctx", err)
+		}
+	})
+
 	t.Run("processes initialize request", func(t *testing.T) {
 		store := &mockPromptStore{prompts: make(map[string]*promptstore.Prompt)}
 		inBuf := &bytes.Buffer{}
@@ -434,7 +451,7 @@ func TestServer_Run(t *testing.T) {
 		// so Run() will complete naturally once it has written the response.
 		done := make(chan error, 1)
 		go func() {
-			done <- server.Run()
+			done <- server.Run(context.Background())
 		}()
 
 		// Wait for Run() to return (signalled by EOF on the input buffer).