feat(coding-agent): added prompt markers to system prompt assembly

- Added explicit prompt markers and wrappers across system templates, including `[env]`, `[role]`, `[coop]`, `[closure]`, and `[now]`.
- Removed `renderTemplate` and `sectionSeparator` flows, deleted `task/template.ts`, and switched to per-task `renderSubagentUserPrompt` rendering.
- Updated system prompt assembly to `shortenPath`-normalize `cwd`, append rendered now metadata, and preserve trailing `[now]` blocks.
- Removed legacy template tests and added prompt-composition tests for ordered `[contract]`->`[project]`->`[now]` blocks and context-only system placement.
- Reworked shared prompt utilities by collapsing consecutive blank lines and removing obsolete `OPENING_HBS`/`LIST_ITEM` helper behavior.

packages/coding-agent/src/task/executor.ts

@@ -139,6 +139,7 @@ export interface ExecutorOptions {
 	agent: AgentDefinition;
 	task: string;
 	assignment?: string;
+	context?: string;
 	description?: string;
 	index: number;
 	id: string;
@@ -994,17 +995,20 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 				skills: options.skills,
 				promptTemplates: options.promptTemplates,
 				workspaceTree: options.workspaceTree,
-				systemPrompt: defaultPrompt => [
-					prompt.render(subagentSystemPromptTemplate, {
-						base: defaultPrompt.join("\n\n"),
+				systemPrompt: defaultPrompt => {
+					const subagentPrompt = prompt.render(subagentSystemPromptTemplate, {
 						agent: agent.systemPrompt,
+						context: options.context?.trim() ?? "",
 						worktree: worktree ?? "",
 						outputSchema: normalizedOutputSchema,
 						contextFile: options.contextFile,
 						ircPeers: ircEnabled ? renderIrcPeerRoster(id) : "",
 						ircSelfId: ircEnabled ? id : "",
-					}),
-				],
+					});
+					return defaultPrompt.length === 0
+						? [subagentPrompt]
+						: [...defaultPrompt.slice(0, -1), subagentPrompt, defaultPrompt[defaultPrompt.length - 1]];
+				},
 				sessionManager,
 				hasUI: false,
 				spawns: spawnsEnv,