Add tmux popup history storage and consolidate state files to XDG_STATE_HOMEv0.19.0

- Add StateDir() helper function respecting XDG_STATE_HOME (~/.local/state/hexai/)
- Implement JSONL-based history storage for tmux popup submissions
  - New history.go with AppendHistory() and GetHistory() functions
  - Store timestamp, agent name, cwd, and submitted text
  - Comprehensive unit tests for history functionality
- Integrate history append into tmux edit workflow after successful submission
- Move logs from /tmp/ to persistent state directory:
  - hexai-lsp.log: ~/.local/state/hexai/hexai-lsp.log
  - hexai-tmux-edit.log: ~/.local/state/hexai/hexai-tmux-edit.log
- Update README.md with File Locations section documenting XDG directories
- Fix pre-existing test failures by isolating project config in unit tests
- Panic on state directory creation failure instead of silent fallback

All unit tests pass. Follows XDG Base Directory Specification for proper
state file management with persistence across reboots.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/internal/appconfig/config.go b/internal/appconfig/config.go
index 63b5ea5..f8c1827 100644
--- a/internal/appconfig/config.go
+++ b/internal/appconfig/config.go
@@ -1270,6 +1270,27 @@ func ConfigPath() (string, error) {
 	return configPath, nil
 }
 
+// StateDir returns the XDG state directory for hexai (~/.local/state/hexai by default).
+// Creates the directory if it doesn't exist. This is used for persistent state data
+// like logs and history that should survive reboots.
+func StateDir() (string, error) {
+	stateHome := os.Getenv("XDG_STATE_HOME")
+	if stateHome == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return "", fmt.Errorf("cannot find user home directory: %v", err)
+		}
+		stateHome = filepath.Join(home, ".local", "state")
+	}
+
+	stateDir := filepath.Join(stateHome, "hexai")
+	if err := os.MkdirAll(stateDir, 0o755); err != nil {
+		return "", fmt.Errorf("cannot create state directory: %v", err)
+	}
+
+	return stateDir, nil
+}
+
 // ProjectConfigFilename is the name of the per-project config file placed at a git repo root.
 const ProjectConfigFilename = ".hexaiconfig.toml"