diff --git a/packages/host/runtime/README.md b/packages/host/runtime/README.md
index f7cf7d9de8..15cff947df 100644
--- a/packages/host/runtime/README.md
+++ b/packages/host/runtime/README.md
@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-host-runtime
 
-Host runtime assembly for `dsh`: `bootHost` composes the core plugin spine (LLM service + DeepSeek adapter, sessions with JSONL persistence and immediate fallback titles, optional first-message model summaries, system prompt, tools, agents, agent loop, workspace instructions, local bash, and the provider-neutral user-interaction service), `createApiProxy` implements the [`dsh-host-apiproxy`](../apiproxy/README.md) contract over that composition, and `startHost` is the one-step shell seam returning `{ api, handler, defaults, ctx, dispose }`.
+Host runtime assembly for `dsh`: `bootHost` composes the core plugin spine (LLM service + DeepSeek adapter, sessions with JSONL persistence, a derived SQLite FTS session-query index, immediate fallback titles, optional first-message model summaries, system prompt, tool and agent registries, agent loop, five workspace-authorized model-facing session-query tools, workspace instructions, local bash, the generic tool-timeout and 50,000-byte spill policies, and the provider-neutral user-interaction service), `createApiProxy` implements the [`dsh-host-apiproxy`](../apiproxy/README.md) contract over that composition, and `startHost` is the one-step shell seam returning `{ api, handler, defaults, ctx, dispose }`.
 
 Which plugins mount and with what defaults is decided only here — shells must not `ctx.plugin` to alter the assembly. `RunningHost.ctx` is a formal seam with exactly two sanctioned uses: mounting protocol front-door plugins (e.g. a future `dsh acp`) and headless session-event subscription; consuming clients must not bypass `api` through it.
 
@@ -8,7 +8,7 @@ Which plugins mount and with what defaults is decided only here — shells must
 
 | Key | Default | Contract |
 |---|---:|---|
-| `persistenceRoot` | (required) | Root directory for JSONL session persistence. |
+| `persistenceRoot` | (required) | Root directory for JSONL session logs and the derived `session-query.db` SQLite FTS index. |
 | `workspaceContext` | (required) | [`AGENTS.md`/`CLAUDE.md` loader](../../context/workspace-context/README.md) config with an explicit `maxBytes`, or `false` to disable it. |
 | `provider` | `'deepseek'` | Default provider route injected as agentOptions on create/resume and reported by `host.describe`. |
 | `model` | `'deepseek-v4-flash'` | Default model id, same single source as `provider`. |
@@ -22,11 +22,81 @@ Unary methods take the narrow `RpcRequest<P>` and echo `request.rpcId`; a prompt
 
 ## Model Experience
 
-Indirectly, through the non-blocking first-message title request owned by [`dsh-session-title-llm`](../../session-title/session-title-llm/README.md) when `sessionTitleLlm` is enabled, the provider/model defaults injected into created and resumed agents, the other model-facing plugins `bootHost` mounts, and the logged [workspace-instruction prefix](../../context/workspace-context/README.md#prompt-shape) when `workspaceContext` is enabled.
+### Prior-history system prompt
+
+#### What the model sees
+
+Every main host agent receives the fixed prior-history guidance below because `bootHost` always mounts the session-query tool plugin.
+
+##### Prior-history guidance
+
+```markdown
+Use session_search to find relevant work from prior sessions, or session_event_search to search earlier events in one session. Search results are cursor-free and workspace-scoped. Follow a useful hit with session_trace, session_event_trace, or session_event_read when you need lineage, relationships, or exact data.
+```
+
+#### Token effect
+
+One fixed concise section is present on every request; `workspaceContext: false` does not remove it.
 
 #### KV Cache effect
 
-No main-request invalidation; when enabled, the auxiliary title request has its own cache behavior and leaves the conversation prefix unchanged.
+The repeated prefix is stable while the fixed host assembly and guidance text are unchanged. Provider cache availability and eviction remain outside the host contract.
+
+### Session-query tool schemas
+
+#### What the model sees
+
+The fixed assembly mounts the generated [`session_search`, `session_event_search`, `session_trace`, `session_event_trace`, and `session_event_read` schemas](../../../docs/tool-catalog.md#deepseek-aidsh-tool-session-query). The schemas expose no workspace path, provider cursor, output page, model-controlled result limit, or timeout argument.
+
+#### Token effect
+
+Five fixed read-only schemas are present on every main-agent request; their cost changes only if the host assembly or an agent-scoped visibility policy changes.
+
+#### KV Cache effect
+
+The schema prefix is stable while visibility, definitions, and order are unchanged. The host makes no claim that a provider will cache or retain that prefix.
+
+### Session-query execution and results
+
+#### What the model sees
+
+Cross-session results require exact equality with the calling session's workspace, while a caller without a workspace can target only itself. `session_search` excludes the calling session, and `session_event_search` on the current session excludes the step performing the call. Both searches are cursor-free, collect at most 100 authorized results, and carry a cooperative 30-second deadline; the three trace/read tools carry caller cancellation but declare no host deadline. Results are plain text. When a final result exceeds 50,000 UTF-8 bytes, the generic spill policy attempts to retain the complete formatted text in a private session-scoped file and replace it with a bounded preview, locator, and retrieval hint; a spill failure leaves the original result visible.
+
+#### Token effect
+
+Call arguments and data-dependent results remain in history until compaction. Search result count is bounded; after a successful spill, only the bounded preview and retrieval notice are resent, while the complete text remains outside model context.
+
+#### KV Cache effect
+
+Calls and results append after the reusable request prefix. Compaction may replace earlier history; timeout or spill outcomes change only the appended result text.
+
+### Workspace instructions
+
+#### What the model sees
+
+When `workspaceContext` is enabled, the model receives the logged [workspace-instruction prefix and loaded file contents](../../context/workspace-context/README.md#prompt-shape), bounded by that configuration's explicit `maxBytes`. Setting `workspaceContext: false` removes this surface.
+
+#### Token effect
+
+Disabled mode adds no tokens. Enabled mode adds the frozen data-dependent baseline to each request, up to the configured byte budget; later discovered, changed, or removed instructions append bounded history messages.
+
+#### KV Cache effect
+
+Prefix-stable within one loop instance because its baseline is frozen. A new or resumed instance recomposes the baseline, while touch-discovered changes during an instance append after the reusable prefix.
+
+### First-message title auxiliary request
+
+#### What the model sees
+
+When `sessionTitleLlm` is enabled, a separate [first-message title model](../../session-title/session-title-first-message-llm/README.md) receives the shared title instruction and a JSON array containing only the first eligible human message. It uses an explicitly configured route or inherits the exact logged main-request route; this auxiliary request does not add text to the main model request or delay its response.
+
+#### Token effect
+
+Disabled by default, so it normally adds no model request. With `sessionTitleLlm: true`, a fresh non-fork session makes at most one automatic request capped at 4,096 input bytes and 64 output tokens; an explicit configuration supplies its own caps. The deterministic fallback remains when the auxiliary request fails.
+
+#### KV Cache effect
+
+The main conversation prefix is unchanged. The auxiliary request has independent, provider-specific cache behavior; the host does not promise cache reuse.
 
 ## Known Limitations and Deferred Work
 
diff --git a/scripts/verify-package-readme-model-experience.ts b/scripts/verify-package-readme-model-experience.ts
index d5fa282a24..5687e51bac 100644
--- a/scripts/verify-package-readme-model-experience.ts
+++ b/scripts/verify-package-readme-model-experience.ts
@@ -66,7 +66,6 @@ const SENTENCE_MODEL_EXPERIENCE: Readonly<Record<string, SentenceContract>> = {
   'packages/fs/fs-sandbox': { kind: 'indirect', reason: 'The provider backend delegates model rendering to dsh-tool-fs.' },
   'packages/hooks/hook-protocol': { kind: 'indirect', reason: 'Only the hook bridge plugins render decoded hook output to a model.' },
   'packages/host/apiproxy': { kind: 'none', reason: 'The wire contract and fetch carriers move already-composed messages and register no model surface.' },
-  'packages/host/runtime': { kind: 'indirect', reason: 'The assembly mounts model-facing plugins and injects provider/model defaults into agents.' },
   'packages/host/webserver': { kind: 'none', reason: 'The HTTP carrier bridges browser and API handler and registers no model surface.' },
   'packages/llm/llm': { kind: 'none', reason: 'The adapter registry forwards already-assembled requests unchanged.' },
   'packages/llm/token-meter': { kind: 'indirect', reason: 'The measurement service leaves model-visible changes to its consumers.' },