feat (memory): Implement new (opt-in) QMD memory backend

docs/concepts/memory.md

@@ -118,6 +118,83 @@ Notes:
 - Only Markdown files are indexed.
 - Symlinks are ignored (files or directories).
 
+### QMD backend (experimental)
+
+Set `memory.backend = "qmd"` to swap the built-in SQLite indexer for
+[QMD](https://github.com/tobi/qmd): a local-first search sidecar that combines
+BM25 + vectors + reranking. Markdown stays the source of truth; OpenClaw shells
+out to QMD for retrieval. Key points:
+
+**Prereqs**
+- Disabled by default. Opt in per-config (`memory.backend = "qmd"`).
+- Install the QMD CLI separately (`bun install -g github.com/tobi/qmd` or grab
+  a release) and make sure the `qmd` binary is on the gateway’s `PATH`.
+- QMD needs an SQLite build that allows extensions (`brew install sqlite` on
+  macOS). The gateway sets `INDEX_PATH`/`QMD_CONFIG_DIR` automatically.
+
+**How the sidecar runs**
+- The gateway writes a self-contained QMD home under
+  `~/.clawdbot/agents/<agentId>/qmd/` (config + cache + sqlite DB).
+- Collections are rewritten from `memory.qmd.paths` (plus default workspace
+  memory files) into `index.yml`, then `qmd update` + `qmd embed` run on boot and
+  on a configurable interval (`memory.qmd.update.interval`, default 5 m).
+- Searches run via `qmd query --json`. If QMD fails or the binary is missing,
+  OpenClaw automatically falls back to the builtin SQLite manager so memory tools
+  keep working.
+
+**Config surface (`memory.qmd.*`)**
+- `command` (default `qmd`): override the executable path.
+- `includeDefaultMemory` (default `true`): auto-index `MEMORY.md` + `memory/**/*.md`.
+- `paths[]`: add extra directories/files (`path`, optional `pattern`, optional
+  stable `name`).
+- `sessions`: opt into session JSONL indexing (`enabled`, `retentionDays`,
+  `exportDir`, `redactToolOutputs`—defaults to redacting tool payloads).
+- `update`: controls refresh cadence (`interval`, `debounceMs`, `onBoot`).
+- `limits`: clamp recall payload (`maxResults`, `maxSnippetChars`,
+  `maxInjectedChars`, `timeoutMs`).
+- `scope`: same schema as [`session.sendPolicy`](/reference/configuration#session-sendpolicy).
+  Default is DM-only (`deny` all, `allow` direct chats); loosen it to surface QMD
+  hits in groups/channels.
+- Snippets sourced outside the workspace show up as
+  `qmd/<collection>/<relative-path>` in `memory_search` results; `memory_get`
+  understands that prefix and reads from the configured QMD collection root.
+- When `memory.qmd.sessions.enabled = true`, OpenClaw exports sanitized session
+  transcripts (User/Assistant turns) into a dedicated QMD collection under
+  `~/.clawdbot/agents/<id>/qmd/sessions/`, so `memory_search` can recall recent
+  conversations without touching the builtin SQLite index.
+- `memory_search` snippets now include a `Source: <path#line>` footer when
+  `memory.citations` is `auto`/`on`; set `memory.citations = "off"` to keep
+  the path metadata internal (the agent still receives the path for
+  `memory_get`, but the snippet text omits the footer and the system prompt
+  warns the agent not to cite it).
+
+**Example**
+
+```json5
+memory: {
+  backend: "qmd",
+  citations: "auto",
+  qmd: {
+    includeDefaultMemory: true,
+    update: { interval: "5m", debounceMs: 15000 },
+    limits: { maxResults: 6, timeoutMs: 4000 },
+    scope: {
+      default: "deny",
+      rules: [{ action: "allow", match: { chatType: "direct" } }]
+    },
+    paths: [
+      { name: "docs", path: "~/notes", pattern: "**/*.md" }
+    ]
+  }
+}
+```
+
+**Citations & fallback**
+- `memory.citations` applies regardless of backend (`auto`/`on`/`off`).
+- When `qmd` runs, we tag `status().backend = "qmd"` so diagnostics show which engine served the results.
+  If the QMD subprocess exits or JSON output can’t be parsed, the search manager logs a warning and
+  returns the builtin provider (existing Markdown embeddings) until QMD recovers.
+
 ### Gemini embeddings (native)
 
 Set the provider to `gemini` to use the Gemini embeddings API directly: