Hop/skills/hop/references/protocol.md

Hop agent protocol

State graph

A accepted
├─ P prompt, persisted before project effects
│  └─ C checkpoint
│     └─ R proposal
└─ P independent prompt

A + R ──land──> A next accepted state

State prefixes:

Prefix	Kind	Meaning
A_	accepted	Canonical project revision
P_	prompt	Exact instruction and pre-effect context
C_	checkpoint	Immutable workspace progress
R_	proposal	Frozen candidate result
F_	failed	Durable failed execution or validation state
X_	cancelled	Durable cancelled state

Prompt, checkpoint, and proposal states may reference identical Git trees while remaining distinct causal occurrences.

Environment contract

Variable	Purpose
HOP_ROOT	Canonical project root containing .hop/hop.db
HOP_STATE_ID	Prompt state authorizing the current instruction
HOP_TASK_ID	Logical task grouping related prompts and attempts
HOP_ATTEMPT_ID	Current agent approach/run
HOP_WORKSPACE	Only directory the agent may modify

Interactive agents may begin without these variables. hop begin returns the equivalent IDs and workspace, while CODEX_THREAD_ID binds later messages in the same Codex task to the existing attempt.

Command contract

Human or controller

hop init
hop start --agent <name> "<exact initial prompt>"
hop env <prompt-state>
hop prompt --from <state> "<exact follow-up prompt>"
hop accept <proposal> -- <final validation command>
hop sync
hop undo

hop start creates the task, attempt, prompt state, and detached workspace before returning. The controller may deliver the prompt only after exit 0.

hop prompt captures a checkpoint of current workspace effects before creating the follow-up prompt state.

Agent

hop begin --agent codex --heredoc <<'HOP_PROMPT_EOF'
<exact current user message>
HOP_PROMPT_EOF
hop state "$HOP_STATE_ID" --json
hop status --json
hop check "$HOP_STATE_ID" -- <command>
hop propose --summary "<summary>" "$HOP_STATE_ID"
hop land <proposal-state> -- <final validation command>

hop check snapshots the attempt and runs the command in a detached worktree materialized from that exact checkpoint. Edits made concurrently in the live workspace do not change the tested tree.

hop propose freezes the current nonignored workspace tree. Later workspace edits cannot change the proposal.

The initial task prompt authorizes the agent to run hop land after successful validation; a second user approval is not required. Manual review is an opt-in mode: stop at the proposal only when the user explicitly asks to review or approve before acceptance. Validation failure, overlap, a stale accepted head, or newly required destructive/external scope also stops automatic acceptance.

hop land is the Desktop operation. It compares paths changed by the proposal with paths accepted since its base, validates and advances accepted state, then safely materializes that tree into the selected visible project root. The root must still match an accepted Hop ancestor, and ignored or untracked destination collisions block before acceptance. Materialization uses a disposable index and never moves HEAD, the active branch, or the user's real index.

hop accept is the controller/kernel operation. It advances SQLite and refs/hop/accepted but intentionally leaves the visible root untouched. hop sync safely catches a stale accepted-ancestor root up to the current accepted state, including projects created with older Hop builds.

hop begin is the Codex Desktop entry point. It initializes Hop when necessary, captures the current message before the agent performs project work, and uses CODEX_THREAD_ID as the default session key. A later hop begin in the same Codex task checkpoints the prior workspace before appending the follow-up prompt state.

Pass the original message to hop begin without model-side redaction. Hop's sanitizer replaces detected credential values before any durable write and returns only typed redaction counts. Do not place the value in any later command, summary, output, or source file.

Exit codes

Code	Meaning
0	Success
1	Git, SQLite, filesystem, or internal error
2	Invalid CLI usage
20	Overlap or conservative conflict block
21	Accepted or attempt head changed during compare-and-swap
22	Validation command failed
23	Visible project root diverged or contains an overwrite collision

A failed hop check or final landing check persists its evidence. A blocked or failed landing does not advance accepted state.

Capture modes

Codex Desktop skill

The user types normally in Codex Desktop. The Hop skill makes hop begin its first project action and then directs every operation into the returned workspace. This is a pre-project-effect boundary: Codex has already received the prompt, but no repository inspection, command, or modification may precede the durable prompt state.

Controller-grade pre-delivery capture

hop init
hop start --agent codex "Add password reset emails"

Use the returned workspace and environment to launch the agent. For example, conceptually:

eval "$(hop env P_...)"
<agent-command> "<the same exact prompt>"

The exact agent command is harness-specific. This stronger mode stores the prompt before the model receives it. A future trusted prompt-submission hook can provide the same boundary inside compatible agent clients.

Failure handling

• Missing Hop environment: run hop begin before project work and use the returned state and workspace.
• Check failure: fix the live workspace, checkpoint/check again, then create a new proposal.
• Review-only request: preserve and report the proposal without landing it.
• Frozen proposal needs changes: record a follow-up prompt; never mutate the stored proposal.
• Overlap on landing: retain both lineages and reconcile through a new prompt against current accepted state.
• Visible-root conflict: preserve the proposal and the user's files. Do not substitute controller-only hop accept; resolve or capture the visible changes, then land again.
• Controller-accepted root is stale: run hop sync; it succeeds only from an accepted ancestor and never overwrites divergence.
• Ref inconsistency: run hop doctor; use hop doctor --repair only outside final validation.
• Secrets: Hop redacts high-confidence provider keys plus contextual tokens, passwords, private keys, authorization headers, and credential-bearing URLs before durable storage. It also sanitizes recorded check commands/output and proposal summaries. Detection is defense in depth, not a substitute for environment variables or a secret manager. Never repeat a detected secret.