Integrate memory system into Ghost

[theantichris]

Summary

Wire the memory storage engine and tools into Ghost's config, registry, and command flow. After this issue, memory is fully functional in both single-shot and chat modes.

Details

Memory is core to Ghost — always on, not a feature flag. The embedding model is a required config value (like the chat model). Configuration is via config file and env vars only, no CLI flags.

Modified files:

cmd/config.go

• Add config bindings (config file + env vars only, no CLI flags):
  • memory.embedding-model — required (like model)
  • memory.dir — optional, default ~/.config/ghost/memory
• Validation: if memory.embedding-model is empty, return error
• New error: ErrNoEmbeddingModel = errors.New("memory cortex requires an embedding model (set via config file or GHOST_MEMORY*EMBEDDING_MODEL environment)")
• Env vars: GHOST_MEMORY*EMBEDDING_MODEL, GHOST_MEMORY*DIR

cmd/memory.go (new)

• Shared helper: initMemoryStore(ollamaURL string, logger *log.Logger) (*memory.Store, error)
• Reads memory.embedding-model and memory.dir from viper
• Creates EmbedFunc closure wrapping llm.Embed()
• Returns initialized *memory.Store

internal/agent/prompt.go

• Add MemoryPrompt constant with instructions for using memory tools
• Add FullSystemPrompt that combines base SystemPrompt + MemoryPrompt

internal/tool/registry.go

• Update NewRegistry signature to accept memoryStore *memory.Store
• Always register MemorySearch and MemorySave tools

internal/tool/registry_test.go

• Update existing NewRegistry calls for new parameter
• Add test for memory tool registration

cmd/root.go

• In run(): call initMemoryStore(), use agent.FullSystemPrompt, pass store to NewRegistry()
• defer memoryStore.Close()
• No new CLI flags

cmd/chat.go

• In runChat(): same wiring — initMemoryStore(), agent.FullSystemPrompt for config.System, store to NewRegistry()
• defer memoryStore.Close()

Config example:

# ~/.config/ghost/config.toml
model = "qwen3:8b"

[memory]
embedding-model = "nomic-embed-text"  # required
# dir = "/custom/path"               # optional

Dependencies

• Add memory_save tool #237 (memory_save tool)
• Add memory_search tool #238 (memory_search tool)

Acceptance Criteria

• Ghost requires memory.embedding-model in config (clear error if missing)
• Memory store initializes on startup in both root and chat commands
• Memory tools registered in tool registry
• System prompt includes memory usage instructions
• ghost "Remember my favorite color is blue" → saves to daily log
• ghost "What's my favorite color?" → searches memory and recalls
• ghost chat → memory works across chat turns
• All existing tests updated and passing
• go test ./... passes

[theantichris]

Config Default: Update memory.dir Path

The default value for memory.dir should be updated from ~/.config/ghost/memory to ~/.local/share/ghost/memory to match the XDG data directory convention.

This keeps memory data alongside conversation data (~/.local/share/ghost/conversations/), maintaining a consistent data layout:

~/.config/ghost/          # Configuration
  config.toml
~/.local/share/ghost/     # User data
  conversations/
  memory/

See also: #236 (storage engine) and #195 (conversation storage).