Create spec for better process management

openspec/changes/improved-opencode-process-management/specs/process-launch/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Server Process Spawning (Modified)
+The plugin SHALL spawn the OpenCode server process using either a configured executable path with default arguments OR a user-defined custom shell command.
+
+**FROM:** 
+The plugin SHALL spawn the OpenCode server process using the configured executable path, port, and hostname when the user initiates server start.
+
+**TO:**
+The plugin SHALL support two execution modes for spawning the OpenCode server process based on the `useCustomCommand` setting.
+
+#### Scenario: Path mode spawn (Modified)
+- **GIVEN** useCustomCommand is false
+- **WHEN** the user starts the server
+- **THEN** the plugin spawns the executable at `opencodePath` with arguments `["serve", "--port", <port>, "--hostname", <hostname>, "--cors", "app://obsidian.md"]`
+- **AND** the process runs with the vault directory as the working directory
+- **AND** the spawn uses `shell: false`
+
+#### Scenario: Custom command mode spawn (New)
+- **GIVEN** useCustomCommand is true
+- **WHEN** the user starts the server
+- **THEN** the plugin spawns `customCommand` as a shell command
+- **AND** the spawn uses `shell: true`
+- **AND** NO additional arguments are appended to the command
+- **AND** the process runs with the vault directory as the working directory
+
+## ADDED Requirements
+
+### Requirement: Command mode selection
+The system SHALL support toggling between path mode and custom command mode via settings.
+
+#### Scenario: Path mode configuration
+- **GIVEN** useCustomCommand is false (default)
+- **WHEN** the server starts
+- **THEN** the system uses the configured opencodePath executable
+- **AND** appends default arguments for port, hostname, and CORS
+
+#### Scenario: Custom command mode configuration
+- **GIVEN** useCustomCommand is true
+- **WHEN** the server starts
+- **THEN** the system uses the configured customCommand string
+- **AND** executes it via shell with no argument manipulation
+
+### Requirement: Executable verification
+The system SHALL verify the executable exists in path mode before attempting to spawn.
+
+#### Scenario: Verify path mode executable
+- **GIVEN** useCustomCommand is false
+- **AND** opencodePath is set to an absolute path
+- **WHEN** the server is about to start
+- **THEN** the system SHALL verify the file exists and is executable
+- **AND** if verification fails, return an error before spawning
+
+#### Scenario: Skip verification for custom command
+- **GIVEN** useCustomCommand is true
+- **WHEN** the server is about to start
+- **THEN** the system SHALL NOT verify the command before spawning
+- **AND** let execution fail naturally if the command is invalid
+
+### Requirement: Settings backward compatibility
+The system SHALL maintain backward compatibility with existing opencodePath configurations.
+
+#### Scenario: Existing path setting works
+- **GIVEN** a configuration from a previous plugin version
+- **AND** opencodePath is set to "/usr/local/bin/opencode"
+- **AND** useCustomCommand is not set (defaults to false)
+- **WHEN** the plugin loads
+- **THEN** the system SHALL use the existing opencodePath
+- **AND** continue working in path mode with default arguments