feat(FN-3612): preserve fusion context in hermes runtime skill forwarding

Merges five commits implementing centralized runtime skill forwarding that preserves Fusion context across the Hermes runtime layer. The engine's `agent-runtime` and `agent-session-helpers` were updated to forward skills at runtime, with `runtime-adapter.ts` and its types extended to carry context.

Fusion-Task-Id: FN-3612

plugins/fusion-plugin-hermes-runtime/README.md

@@ -36,7 +36,9 @@ Because we drive the CLI's `chat -q` mode:
 - **No per-token streaming.** Hermes buffers output through prompt_toolkit; the full response arrives once the process exits. `onText` is called exactly once per turn.
 - **No reasoning/thinking deltas.** `-Q` mode suppresses them. If you need streaming + reasoning, switch to Hermes's ACP mode (not yet implemented in this plugin).
 - **No tool-call hooks.** Hermes runs tools internally; Fusion only sees the final assistant text. Use `yolo: true` to skip Hermes's interactive approval prompts in non-interactive sessions.
-- **`AgentRuntimeOptions.cwd`, `tools`, `skills`, `sessionManager`, etc. are ignored** — Hermes's own session/tools/skills systems handle these.
+- **No JS tool callbacks.** `customTools` callback functions are still not executable through Hermes CLI mode; Hermes runs its own tool layer and Fusion receives final text.
+- **Fusion context is prompt-mediated.** The engine forwards requested Fusion skill names into `skills`, and the adapter prepends Fusion system/runtime context on the first turn of each session so capability expectations (for example messaging/delegation flows) are not silently dropped on non-pi runtimes.
+- `AgentRuntimeOptions.cwd` / `sessionManager` are still adapter-noops in CLI mode.
 
 ## Settings
 

plugins/fusion-plugin-hermes-runtime/src/__tests__/runtime-adapter.test.ts

@@ -61,7 +61,8 @@ describe("HermesRuntimeAdapter — promptWithFallback", () => {
 
     expect(mockInvoke).toHaveBeenCalledTimes(1);
     const [prompt, settings, resumeId] = mockInvoke.mock.calls[0];
-    expect(prompt).toBe("first prompt");
+    expect(prompt).toContain("User request:\nfirst prompt");
+    expect(prompt).toContain("Fusion runtime context:");
     expect(settings.model).toBe("claude-sonnet-4-5");
     expect(resumeId).toBeUndefined();
     expect(onText).toHaveBeenCalledWith("hello from hermes");
@@ -78,7 +79,8 @@ describe("HermesRuntimeAdapter — promptWithFallback", () => {
     await adapter.promptWithFallback(session, "p1");
     await adapter.promptWithFallback(session, "p2");
 
-    const [, , resume2] = mockInvoke.mock.calls[1];
+    const [prompt2, , resume2] = mockInvoke.mock.calls[1];
+    expect(prompt2).toBe("p2");
     expect(resume2).toBe("20260427_120000_abc123");
   });
 

plugins/fusion-plugin-hermes-runtime/src/runtime-adapter.ts

@@ -16,6 +16,28 @@ import type {
   HermesStreamSession,
 } from "./types.js";
 
+function buildRuntimeContextSection(options: AgentRuntimeOptions): string {
+  const skillNames = Array.isArray(options.skills) ? options.skills.filter((value): value is string => typeof value === "string" && value.trim().length > 0) : [];
+  const skillSelection = options.skillSelection as { requestedSkillNames?: unknown } | undefined;
+  const selectionSkillNames = Array.isArray(skillSelection?.requestedSkillNames)
+    ? skillSelection.requestedSkillNames.filter((value): value is string => typeof value === "string" && value.trim().length > 0)
+    : [];
+  const mergedSkills = skillNames.length > 0 ? skillNames : selectionSkillNames;
+
+  const lines: string[] = [
+    "Fusion runtime context:",
+    `- Tool mode: ${options.tools ?? "coding"}`,
+  ];
+
+  if (mergedSkills.length > 0) {
+    lines.push(`- Requested skills: ${mergedSkills.join(", ")}`);
+  }
+
+  lines.push("- If fn_* tools are available in your runtime, use them directly for coordination/memory/task actions.");
+
+  return lines.join("\n");
+}
+
 export class HermesRuntimeAdapter implements AgentRuntime {
   readonly id = "hermes";
   readonly name = "Hermes Runtime";
@@ -43,6 +65,8 @@ export class HermesRuntimeAdapter implements AgentRuntime {
         onToolStart: options.onToolStart,
         onToolEnd: options.onToolEnd,
       },
+      runtimeContext: options.runtimeContext,
+      fusedSystemPrompt: [options.systemPrompt.trim(), buildRuntimeContextSection(options).trim()].filter((part) => part.length > 0).join("\n\n"),
       dispose: () => undefined,
     };
 
@@ -55,7 +79,10 @@ export class HermesRuntimeAdapter implements AgentRuntime {
     _options?: unknown,
   ): Promise<void> {
     const resumeId = session.sessionId || undefined;
-    const result = await invokeHermesCli(prompt, this.settings, resumeId);
+    const promptWithContext = resumeId
+      ? prompt
+      : `${session.fusedSystemPrompt}\n\nUser request:\n${prompt}`;
+    const result = await invokeHermesCli(promptWithContext, this.settings, resumeId);
 
     session.sessionId = result.sessionId;
     session.lastModelDescription = this.describeFromSettings();

plugins/fusion-plugin-hermes-runtime/src/types.ts

@@ -12,6 +12,13 @@ export interface HermesCallbacks {
   onToolEnd?: (toolName: string, isError: boolean, result?: unknown) => void;
 }
 
+export interface HermesRuntimeContext {
+  sessionPurpose?: string;
+  toolMode?: "coding" | "readonly";
+  customToolNames?: string[];
+  requestedSkillNames?: string[];
+}
+
 export interface HermesStreamSession {
   model: unknown;
   systemPrompt: string;
@@ -22,6 +29,8 @@ export interface HermesStreamSession {
   lastModelDescription: string;
   callbacks: HermesCallbacks;
   usage?: unknown;
+  runtimeContext?: HermesRuntimeContext;
+  fusedSystemPrompt: string;
   dispose(): void;
 }
 
@@ -49,6 +58,7 @@ export interface AgentRuntimeOptions {
   sessionManager?: unknown;
   skillSelection?: unknown;
   skills?: string[];
+  runtimeContext?: HermesRuntimeContext;
 }
 
 /** Result of creating a session. */