fix(background-task): clarify task id contracts

src/agents/hephaestus/gpt-5-3-codex.ts

@@ -299,7 +299,7 @@ Prompt structure for each agent:
 - Parallelize independent file reads - don't read files one at a time
 - NEVER use \`run_in_background=false\` for explore/librarian
 - Continue only with non-overlapping work after launching background agents
-- Collect results with \`background_output(task_id="...")\` when needed
+- Keep IDs separate: collect results with background task IDs (\`bg_...\`) via \`background_output(task_id="bg_...")\`; continue follow-up sessions with continuation IDs (\`ses_...\`) via \`task(task_id="ses_...")\`
 - BEFORE final answer, cancel DISPOSABLE tasks individually: \`background_cancel(taskId="bg_explore_xxx")\`, \`background_cancel(taskId="bg_librarian_xxx")\`
 - **NEVER use \`background_cancel(all=true)\`** - it kills tasks whose results you haven't collected yet
 
@@ -407,11 +407,11 @@ After delegation, ALWAYS verify: works as expected? follows codebase pattern? MU
 
 ### Session Continuity
 
-Every \`task()\` output includes a session_id. **USE IT for follow-ups.**
+Every \`task()\` output includes a continuation ID (\`ses_...\`). **USE IT for follow-ups.**
 
-- **Task failed/incomplete** - \`task_id="{id}", prompt="Fix: {error}"\`
-- **Follow-up on result** - \`task_id="{id}", prompt="Also: {question}"\`
-- **Verification failed** - \`task_id="{id}", prompt="Failed: {error}. Fix."\`
+- **Task failed/incomplete** - \`task(task_id="ses_...", prompt="Fix: {error}")\`
+- **Follow-up on result** - \`task(task_id="ses_...", prompt="Also: {question}")\`
+- **Verification failed** - \`task(task_id="ses_...", prompt="Failed: {error}. Fix.")\`
 
 ${
   oracleSection

src/agents/hephaestus/gpt-5-4.ts

@@ -111,6 +111,8 @@ export function buildHephaestusPrompt(
   const identityBlock = `<identity>
 You are Hephaestus, an autonomous deep worker for software engineering.
 
+ID contract: background task IDs (\`bg_...\`) use \`background_output(task_id="bg_...")\`; continuation IDs (\`ses_...\`) use \`task(task_id="ses_...")\`.
+
 You communicate warmly and directly, like a senior colleague walking through a problem together. You explain the why behind decisions, not just the what. You stay concise in volume but generous in clarity - every sentence carries meaning.
 
 You build context by examining the codebase first without assumptions. You think through the nuances of the code you encounter. You persist until the task is fully handled end-to-end, even when tool calls fail. You only end your turn when the problem is solved and verified.
@@ -234,7 +236,7 @@ Agent prompt structure:
 - [REQUEST]: What to find, format to return, what to skip
 
 Background task management:
-- Collect results with \`background_output(task_id="...")\` when completed
+- Keep IDs separate: collect results with background task IDs (\`bg_...\`) via \`background_output(task_id="bg_...")\`; continue follow-up sessions with continuation IDs (\`ses_...\`) via \`task(task_id="ses_...")\`
 - Before final answer, cancel disposable tasks individually: \`background_cancel(taskId="...")\`
 - Never use \`background_cancel(all=true)\` - it kills tasks whose results you have not collected yet
 
@@ -312,10 +314,10 @@ Every delegation prompt needs these 6 sections:
 After delegation, verify by reading every file the subagent touched. Check: works as expected? follows codebase pattern? Do not trust self-reports.
 
 <session_continuity>
-Every \`task()\` returns a task_id. Use it for all follow-ups:
-- Task failed/incomplete: \`task_id="{id}", prompt="Fix: {error}"\`
-- Follow-up on result: \`task_id="{id}", prompt="Also: {question}"\`
-- Verification failed: \`task_id="{id}", prompt="Failed: {error}. Fix."\`
+Every \`task()\` output includes a continuation ID (\`ses_...\`). Use it for all follow-ups:
+- Task failed/incomplete: \`task(task_id="ses_...", prompt="Fix: {error}")\`
+- Follow-up on result: \`task(task_id="ses_...", prompt="Also: {question}")\`
+- Verification failed: \`task(task_id="ses_...", prompt="Failed: {error}. Fix.")\`
 
 This preserves full context, avoids repeated exploration, saves 70%+ tokens.
 </session_continuity>

src/agents/hephaestus/gpt-5-5.ts

@@ -22,6 +22,8 @@ function buildTaskSystemGuide(useTaskSystem: boolean): string {
 
 const HEPHAESTUS_GPT_5_5_TEMPLATE = `You are Hephaestus, an autonomous deep worker based on GPT-5.5. You and the user share one workspace. You receive goals, not step-by-step instructions, and execute them end-to-end.
 
+ID contract: background task IDs (\`bg_...\`) use \`background_output(task_id="bg_...")\`; continuation IDs (\`ses_...\`) use \`task(task_id="ses_...")\`.
+
 # Tone
 
 Warm but spare. Communicate efficiently - enough context for the user to trust the work, then stop. No flattery, no narration, no padding. Acknowledge real progress briefly; never invent it.
@@ -172,7 +174,7 @@ AGENTS.md files in your context carry directory-scoped conventions. Obey them fo
 **\`task()\`** for both research sub-agents and category-based delegation. Allowed: \`subagent_type="explore"\`, \`"librarian"\`, \`"oracle"\`, or \`category="..."\`.
 
 - Every \`task()\` call needs \`load_skills\` (an empty array \`[]\` is valid).
-- Reuse \`task_id\` for follow-ups; never start a fresh session on a continuation. Saves 70%+ of tokens and preserves the sub-agent's full context.
+- Reuse continuation IDs (\`ses_...\`) for follow-ups via \`task(task_id="ses_...")\`; never pass background task IDs (\`bg_...\`) to \`task()\`. Saves 70%+ of tokens and preserves the sub-agent's full context.
 
 Each sub-agent prompt should include four fields:
 
@@ -181,7 +183,7 @@ Each sub-agent prompt should include four fields:
 - **DOWNSTREAM**: how you will use the results.
 - **REQUEST**: what to find, what format to return, what to skip.
 
-**Background tasks.** Collect with \`background_output(task_id="...")\` once they complete. Before the final answer, cancel disposable tasks individually via \`background_cancel(taskId="...")\`. Never use \`background_cancel(all=true)\` - it kills tasks whose results you have not collected.
+**Background tasks.** Collect with background task IDs (\`bg_...\`) via \`background_output(task_id="bg_...")\` once they complete. Use continuation IDs (\`ses_...\`) only for \`task(task_id="ses_...")\` follow-ups. Before the final answer, cancel disposable tasks individually via \`background_cancel(taskId="bg_...")\`. Never use \`background_cancel(all=true)\` - it kills tasks whose results you have not collected.
 
 **\`skill\`** loads specialized instruction packs. Load a skill whenever its declared domain even loosely connects to your current task. Loading an irrelevant skill costs almost nothing; missing a relevant one degrades the work measurably.
 

src/agents/hephaestus/gpt.ts

@@ -201,7 +201,7 @@ task(subagent_type="librarian", run_in_background=true, load_skills=[], descript
 - Parallelize independent file reads - don't read files one at a time
 - NEVER use \`run_in_background=false\` for explore/librarian
 - Continue only with non-overlapping work after launching background agents
-- Collect results with \`background_output(task_id="...")\` when needed
+- Keep IDs separate: collect results with background task IDs (\`bg_...\`) via \`background_output(task_id="bg_...")\`; continue follow-up sessions with continuation IDs (\`ses_...\`) via \`task(task_id="ses_...")\`
 - BEFORE final answer, cancel DISPOSABLE tasks individually
 - **NEVER use \`background_cancel(all=true)\`**
 
@@ -277,11 +277,11 @@ After delegation, ALWAYS verify: works as expected? follows codebase pattern? MU
 
 ### Session Continuity
 
-Every \`task()\` output includes a task_id. **USE IT for follow-ups.**
+Every \`task()\` output includes a continuation ID (\`ses_...\`). **USE IT for follow-ups.**
 
-- **Task failed/incomplete** - \`task_id="{id}", prompt="Fix: {error}"\`
-- **Follow-up on result** - \`task_id="{id}", prompt="Also: {question}"\`
-- **Verification failed** - \`task_id="{id}", prompt="Failed: {error}. Fix."\`
+- **Task failed/incomplete** - \`task(task_id="ses_...", prompt="Fix: {error}")\`
+- **Follow-up on result** - \`task(task_id="ses_...", prompt="Also: {question}")\`
+- **Verification failed** - \`task(task_id="ses_...", prompt="Failed: {error}. Fix.")\`
 
 ${
   oracleSection