paperclip/doc/execution-semantics.md

Execution Semantics

Status: Current implementation guide Date: 2026-04-13 Audience: Product and engineering

This document explains how Paperclip interprets issue assignment, issue status, execution runs, wakeups, parent/sub-issue structure, and blocker relationships.

doc/SPEC-implementation.md remains the V1 contract. This document is the detailed execution model behind that contract.

1. Core Model

Paperclip separates four concepts that are easy to blur together:

1. structure: parent/sub-issue relationships
2. dependency: blocker relationships
3. ownership: who is responsible for the issue now
4. execution: whether the control plane currently has a live path to move the issue forward

The system works best when those are kept separate.

2. Assignee Semantics

An issue has at most one assignee.

• assigneeAgentId means the issue is owned by an agent
• assigneeUserId means the issue is owned by a human board user
• both cannot be set at the same time

This is a hard invariant. Paperclip is single-assignee by design.

3. Status Semantics

Paperclip issue statuses are not just UI labels. They imply different expectations about ownership and execution.

backlog

The issue is not ready for active work.

• no execution expectation
• no pickup expectation
• safe resting state for future work

todo

The issue is actionable but not actively claimed.

• it may be assigned or unassigned
• no checkout/execution lock is required yet
• for agent-assigned work, Paperclip may still need a wake path to ensure the assignee actually sees it

in_progress

The issue is actively owned work.

• requires an assignee
• for agent-owned issues, this is a strict execution-backed state
• for user-owned issues, this is a human ownership state and is not backed by heartbeat execution

For agent-owned issues, in_progress should not be allowed to become a silent dead state.

blocked

The issue cannot proceed until something external changes.

This is the right state for:

• waiting on another issue
• waiting on a human decision
• waiting on an external dependency or system
• work that automatic recovery could not safely continue

in_review

Execution work is paused because the next move belongs to a reviewer or approver, not the current executor.

done

The work is complete and terminal.

cancelled

The work will not continue and is terminal.

4. Agent-Owned vs User-Owned Execution

The execution model differs depending on assignee type.

Agent-owned issues

Agent-owned issues are part of the control plane's execution loop.

• Paperclip can wake the assignee
• Paperclip can track runs linked to the issue
• Paperclip can recover some lost execution state after crashes/restarts

User-owned issues

User-owned issues are not executed by the heartbeat scheduler.

• Paperclip can track the ownership and status
• Paperclip cannot rely on heartbeat/run semantics to keep them moving
• stranded-work reconciliation does not apply to them

This is why in_progress can be strict for agents without forcing the same runtime rules onto human-held work.

5. Checkout and Active Execution

Checkout is the bridge from issue ownership to active agent execution.

• checkout is required to move an issue into agent-owned in_progress
• checkoutRunId represents issue-ownership lock for the current agent run
• executionRunId represents the currently active execution path for the issue

These are related but not identical:

• checkoutRunId answers who currently owns execution rights for the issue
• executionRunId answers which run is actually live right now

Paperclip already clears stale execution locks and can adopt some stale checkout locks when the original run is gone.

6. Parent/Sub-Issue vs Blockers

Paperclip uses two different relationships for different jobs.

Parent/Sub-Issue (parentId)

This is structural.

Use it for:

• work breakdown
• rollup context
• explaining why a child issue exists
• waking the parent assignee when all direct children become terminal

Do not treat parentId as execution dependency by itself.

Blockers (blockedByIssueIds)

This is dependency semantics.

Use it for:

• "this issue cannot continue until that issue changes state"
• explicit waiting relationships
• automatic wakeups when all blockers resolve

If a parent is truly waiting on a child, model that with blockers. Do not rely on the parent/child relationship alone.

7. Consistent Execution Path Rules

For agent-assigned, non-terminal, actionable issues, Paperclip should not leave work in a state where nobody is working it and nothing will wake it.

The relevant execution path depends on status.

Agent-assigned todo

This is dispatch state: ready to start, not yet actively claimed.

A healthy dispatch state means at least one of these is true:

• the issue already has a queued/running wake path
• the issue is intentionally resting in todo after a successful agent heartbeat, not after an interrupted dispatch
• the issue has been explicitly surfaced as stranded

Agent-assigned in_progress

This is active-work state.

A healthy active-work state means at least one of these is true:

• there is an active run for the issue
• there is already a queued continuation wake
• the issue has been explicitly surfaced as stranded

8. Crash and Restart Recovery

Paperclip now treats crash/restart recovery as a stranded-assigned-work problem, not just a stranded-run problem.

There are two distinct failure modes.

8.1 Stranded assigned todo

Example:

• issue is assigned to an agent
• status is todo
• the original wake/run died during or after dispatch
• after restart there is no queued wake and nothing picks the issue back up

Recovery rule:

• if the latest issue-linked run failed/timed out/cancelled and no live execution path remains, Paperclip queues one automatic assignment recovery wake
• if that recovery wake also finishes and the issue is still stranded, Paperclip moves the issue to blocked and posts a visible comment

This is a dispatch recovery, not a continuation recovery.

8.2 Stranded assigned in_progress

Example:

• issue is assigned to an agent
• status is in_progress
• the live run disappeared
• after restart there is no active run and no queued continuation

Recovery rule:

• Paperclip queues one automatic continuation wake
• if that continuation wake also finishes and the issue is still stranded, Paperclip moves the issue to blocked and posts a visible comment

This is an active-work continuity recovery.

9. Startup and Periodic Reconciliation

Startup recovery and periodic recovery are different from normal wakeup delivery.

On startup and on the periodic recovery loop, Paperclip now does three things in sequence:

1. reap orphaned running runs
2. resume persisted queued runs
3. reconcile stranded assigned work

That last step is what closes the gap where issue state survives a crash but the wake/run path does not.

10. What This Does Not Mean

These semantics do not change V1 into an auto-reassignment system.

Paperclip still does not:

• automatically reassign work to a different agent
• infer dependency semantics from parentId alone
• treat human-held work as heartbeat-managed execution

The recovery model is intentionally conservative:

• preserve ownership
• retry once when the control plane lost execution continuity
• escalate visibly when the system cannot safely keep going

11. Practical Interpretation

For a board operator, the intended meaning is:

• agent-owned in_progress should mean "this is live work or clearly surfaced as a problem"
• agent-owned todo should not stay assigned forever after a crash with no remaining wake path
• parent/sub-issue explains structure
• blockers explain waiting

That is the execution contract Paperclip should present to operators.