Harness — Long-Running Agent Framework

Executable protocol enabling any agent task to run continuously across multiple sessions with automatic progress recovery, task dependency resolution, failure rollback, and standardized error handling.

Design Principles

Design for the agent, not the human — Test output, docs, and task structure are the agent's primary interface
Progress files ARE the context — When context window resets, progress files + git history = full recovery
Premature completion is the #1 failure mode — Structured task lists with explicit completion criteria prevent declaring victory early
Standardize everything grep-able — ERROR on same line, structured timestamps, consistent prefixes
Fast feedback loops — Pre-compute stats, run smoke tests before full validation
Idempotent everything — Init scripts, task execution, environment setup must all be safe to re-run
Fail safe, not fail silent — Every failure must have an explicit recovery strategy

Commands

/harness init <project-path>     # Initialize harness files in project
/harness run                     # Start/resume the infinite loop
/harness status                  # Show current progress and stats
/harness add "task description"  # Add a task to the list

Activation Marker

Hooks only take effect when

.harness-active

marker file exists in the harness root (same directory as

harness-tasks.json

). Hook 注册配置在

hooks/hooks.json

。

/harness init

and

/harness run

MUST create this marker:

touch <project-path>/.harness-active

When all tasks complete (no pending/in_progress/retryable left), remove it:
```
rm <project-path>/.harness-active
```
Without this marker, all hooks are no-ops — they exit 0 immediately

Progress Persistence (Dual-File System)

Maintain two files in the project working directory:

harness-progress.txt (Append-Only Log)

Free-text log of all agent actions across sessions. Never truncate.

[2025-07-01T10:00:00Z] [SESSION-1] INIT Harness initialized for project /path/to/project
[2025-07-01T10:00:05Z] [SESSION-1] INIT Environment health check: PASS
[2025-07-01T10:00:10Z] [SESSION-1] LOCK acquired (pid=12345)
[2025-07-01T10:00:11Z] [SESSION-1] Starting [task-001] Implement user authentication (base=def5678)
[2025-07-01T10:05:00Z] [SESSION-1] CHECKPOINT [task-001] step=2/4 "auth routes created, tests pending"
[2025-07-01T10:15:30Z] [SESSION-1] Completed [task-001] (commit abc1234)
[2025-07-01T10:15:31Z] [SESSION-1] Starting [task-002] Add rate limiting (base=abc1234)
[2025-07-01T10:20:00Z] [SESSION-1] ERROR [task-002] [TASK_EXEC] Redis connection refused
[2025-07-01T10:20:01Z] [SESSION-1] ROLLBACK [task-002] git reset --hard abc1234
[2025-07-01T10:20:02Z] [SESSION-1] STATS tasks_total=5 completed=1 failed=1 pending=3 blocked=0 attempts_total=2 checkpoints=1

harness-tasks.json (Structured State)

json

{
  "version": 2,
  "created": "2025-07-01T10:00:00Z",
  "session_config": {
    "concurrency_mode": "exclusive",
    "max_tasks_per_session": 20,
    "max_sessions": 50
  },
  "tasks": [
    {
      "id": "task-001",
      "title": "Implement user authentication",
      "status": "completed",
      "priority": "P0",
      "depends_on": [],
      "attempts": 1,
      "max_attempts": 3,
      "started_at_commit": "def5678",
      "validation": {
        "command": "npm test -- --testPathPattern=auth",
        "timeout_seconds": 300
      },
      "on_failure": {
        "cleanup": null
      },
      "error_log": [],
      "checkpoints": [],
      "completed_at": "2025-07-01T10:15:30Z"
    },
    {
      "id": "task-002",
      "title": "Add rate limiting",
      "status": "failed",
      "priority": "P1",
      "depends_on": [],
      "attempts": 1,
      "max_attempts": 3,
      "started_at_commit": "abc1234",
      "validation": {
        "command": "npm test -- --testPathPattern=rate-limit",
        "timeout_seconds": 120
      },
      "on_failure": {
        "cleanup": "docker compose down redis"
      },
      "error_log": ["[TASK_EXEC] Redis connection refused"],
      "checkpoints": [],
      "completed_at": null
    },
    {
      "id": "task-003",
      "title": "Add OAuth providers",
      "status": "pending",
      "priority": "P1",
      "depends_on": ["task-001"],
      "attempts": 0,
      "max_attempts": 3,
      "started_at_commit": null,
      "validation": {
        "command": "npm test -- --testPathPattern=oauth",
        "timeout_seconds": 180
      },
      "on_failure": {
        "cleanup": null
      },
      "error_log": [],
      "checkpoints": [],
      "completed_at": null
    }
  ],
  "session_count": 1,
  "last_session": "2025-07-01T10:20:02Z"
}

Task statuses:

pending

→

in_progress

(transient, set only during active execution) →

completed

failed

. A task found as

in_progress

at session start means the previous session was interrupted — handle via Context Window Recovery Protocol.

In concurrent mode (see Concurrency Control), tasks may also carry claim metadata:

claimed_by

and

lease_expires_at

(ISO timestamp).

Session boundary: A session starts when the agent begins executing the Session Start protocol and ends when a Stopping Condition is met or the context window resets. Each session gets a unique

SESSION-N

identifier (N =

session_count

after increment).

Concurrency Control

Before modifying

harness-tasks.json

, acquire an exclusive lock using portable

mkdir

(atomic on all POSIX systems, works on both macOS and Linux):

bash

# Acquire lock (fail fast if another agent is running)
# Lock key must be stable even if invoked from a subdirectory.
ROOT="$PWD"
SEARCH="$PWD"
while [ "$SEARCH" != "/" ] && [ ! -f "$SEARCH/harness-tasks.json" ]; do
  SEARCH="$(dirname "$SEARCH")"
done
if [ -f "$SEARCH/harness-tasks.json" ]; then
  ROOT="$SEARCH"
fi

PWD_HASH="$(
  printf '%s' "$ROOT" |
    (shasum -a 256 2>/dev/null || sha256sum 2>/dev/null) |
    awk '{print $1}' |
    cut -c1-16
)"
LOCKDIR="/tmp/harness-${PWD_HASH:-unknown}.lock"
if ! mkdir "$LOCKDIR" 2>/dev/null; then
  # Check if lock holder is still alive
  LOCK_PID=$(cat "$LOCKDIR/pid" 2>/dev/null)
  if [ -n "$LOCK_PID" ] && kill -0 "$LOCK_PID" 2>/dev/null; then
    echo "ERROR: Another harness session is active (pid=$LOCK_PID)"; exit 1
  fi
  # Stale lock — atomically reclaim via mv to avoid TOCTOU race
  STALE="$LOCKDIR.stale.$$"
  if mv "$LOCKDIR" "$STALE" 2>/dev/null; then
    rm -rf "$STALE"
    mkdir "$LOCKDIR" || { echo "ERROR: Lock contention"; exit 1; }
    echo "WARN: Removed stale lock${LOCK_PID:+ from pid=$LOCK_PID}"
  else
    echo "ERROR: Another agent reclaimed the lock"; exit 1
  fi
fi
echo "$$" > "$LOCKDIR/pid"
trap 'rm -rf "$LOCKDIR"' EXIT

Log lock acquisition:

[timestamp] [SESSION-N] LOCK acquired (pid=<PID>)

Log lock release:

[timestamp] [SESSION-N] LOCK released

Modes:

Exclusive (default): hold the lock for the entire session (the
```
trap EXIT
```
handler releases it automatically). Any second session in the same state root fails fast.
Concurrent (opt-in via
session_config.concurrency_mode: "concurrent"
): treat this as a state transaction lock. Hold it only while reading/modifying/writing
```
harness-tasks.json
```
(including
```
.bak
```
/
```
.tmp
```
) and appending to
```
harness-progress.txt
```
. Release it immediately before doing real work.

Concurrent mode invariants:

All workers MUST point at the same state root (the directory that contains
```
harness-tasks.json
```
). If you are using separate worktrees/clones, pin it explicitly (e.g.,
```
HARNESS_STATE_ROOT=/abs/path/to/state-root
```
).
Task selection is advisory; the real gate is atomic claim under the lock: set
```
status="in_progress"
```
, set
```
claimed_by
```
(stable worker id, e.g.,
```
HARNESS_WORKER_ID
```
), set
```
lease_expires_at
```
. If claim fails (already
```
in_progress
```
with a valid lease), pick another eligible task and retry.
Never run two workers in the same git working directory. Use separate worktrees/clones. Otherwise rollback (
```
git reset --hard
```
/
```
git clean -fd
```
) will destroy other workers.

Infinite Loop Protocol

Session Start (Execute Every Time)

Read state: Read last 200 lines of
```
harness-progress.txt
```
+ full
```
harness-tasks.json
```
. If JSON is unparseable, see JSON corruption recovery in Error Handling.
Read git: Run
```
git log --oneline -20
```
and
```
git diff --stat
```
to detect uncommitted work
Acquire lock (mode-dependent): Exclusive mode fails if another session is active. Concurrent mode uses the lock only for state transactions.
Recover interrupted tasks (see Context Window Recovery below)
Health check: Run
```
harness-init.sh
```
if it exists
Track session: Increment
```
session_count
```
in JSON. Check
```
session_count
```
against
```
max_sessions
```
— if reached, log STATS and STOP. Initialize per-session task counter to 0.
Pick next task using Task Selection Algorithm below

Task Selection Algorithm

Before selecting, run dependency validation:

Cycle detection: For each non-completed task, walk
```
depends_on
```
transitively. If any task appears in its own chain, mark it
```
failed
```
with
```
[DEPENDENCY] Circular dependency detected: task-A -> task-B -> task-A
```
. Self-references (
```
depends_on
```
includes own id) are also cycles.
Blocked propagation: If a task's
```
depends_on
```
includes a task that is
```
failed
```
and will never be retried (either
```
attempts >= max_attempts
```
OR its
```
error_log
```
contains a
```
[DEPENDENCY]
```
entry), mark the blocked task as
```
failed
```
with
```
[DEPENDENCY] Blocked by failed task-XXX
```
. Repeat until no more tasks can be propagated.

Then pick the next task in this priority order:

Tasks with
```
status: "pending"
```
where ALL
```
depends_on
```
tasks are
```
completed
```
— sorted by
```
priority
```
(P0 > P1 > P2), then by
```
id
```
(lowest first)
Tasks with
```
status: "failed"
```
where
```
attempts < max_attempts
```
and ALL
```
depends_on
```
are
```
completed
```
— sorted by priority, then oldest failure first
If no eligible tasks remain → log final STATS → STOP

Task Execution Cycle

For each task, execute this exact sequence:

Claim (atomic, under lock): Record
```
started_at_commit
```
= current HEAD hash. Set status to
```
in_progress
```
, set
```
claimed_by
```
, set
```
lease_expires_at
```
, log
```
Starting [<task-id>] <title> (base=<hash>)
```
. If the task is already claimed (
```
in_progress
```
with a valid lease), pick another eligible task and retry.
Execute with checkpoints: Perform the work. After each significant step, log:
```
[timestamp] [SESSION-N] CHECKPOINT [task-id] step=M/N "description of what was done"
```
Also append to the task's
```
checkpoints
```
array:
```
{ "step": M, "total": N, "description": "...", "timestamp": "ISO" }
```
. In concurrent mode, renew the lease at each checkpoint (push
```
lease_expires_at
```
forward).
Validate: Run the task's
```
validation.command
```
with a timeout wrapper (prefer
```
timeout
```
; on macOS use
```
gtimeout
```
from coreutils). If
```
validation.command
```
is empty/null, log
```
ERROR [<task-id>] [CONFIG] Missing validation.command
```
and STOP — do not declare completion without an objective check. Before running, verify the command exists (e.g.,
```
command -v <binary>
```
) — if missing, treat as
```
ENV_SETUP
```
error.
- Command exits 0 → PASS
- Command exits non-zero → FAIL
- Command exceeds timeout → TIMEOUT
Record outcome:
- Success: status=
```
completed
```
  , set
```
completed_at
```
  , log
```
Completed [<task-id>] (commit <hash>)
```
  , git commit
- Failure: increment
```
attempts
```
  , append error to
```
error_log
```
  . Verify
```
started_at_commit
```
  exists via
```
git cat-file -t <hash>
```
  — if missing, mark failed at max_attempts. Otherwise execute
```
git reset --hard <started_at_commit>
```
  and
```
git clean -fd
```
  to rollback ALL commits and remove untracked files. Execute
```
on_failure.cleanup
```
  if defined. Log
```
ERROR [<task-id>] [<category>] <message>
```
  . Set status=
```
failed
```
  (Task Selection Algorithm pass 2 handles retries when attempts < max_attempts)
Track: Increment per-session task counter. If
```
max_tasks_per_session
```
reached, log STATS and STOP.
Continue: Immediately pick next task (zero idle time)

Stopping Conditions

All tasks
```
completed
```
All remaining tasks
```
failed
```
at max_attempts or blocked by failed dependencies
```
session_config.max_tasks_per_session
```
reached for this session
```
session_config.max_sessions
```
reached across all sessions
User interrupts

Context Window Recovery Protocol

When a new session starts and finds a task with

status: "in_progress"

Exclusive mode: treat this as an interrupted previous session and run the Recovery Protocol below.
Concurrent mode: only recover a task if either (a)
```
claimed_by
```
matches this worker, or (b)
```
lease_expires_at
```
is in the past (stale lease). Otherwise, treat it as owned by another worker and do not modify it.

Check git state:

bash

git diff --stat          # Uncommitted changes?
git log --oneline -5     # Recent commits since task started?
git stash list           # Any stashed work?

Check checkpoints: Read the task's
```
checkpoints
```
array to determine last completed step
Decision matrix (verify recent commits belong to this task by checking commit messages for the task-id):

Uncommitted?	Recent task commits?	Checkpoints?	Action
No	No	None	Mark `failed` with `[SESSION_TIMEOUT] No progress detected` , increment attempts
No	No	Some	Verify file state matches checkpoint claims. If files reflect checkpoint progress, resume from last step. If not, mark `failed` — work was lost
No	Yes	Any	Run `validation.command` . If passes → mark `completed` . If fails → `git reset --hard <started_at_commit>` , mark `failed`
Yes	No	Any	Run validation WITH uncommitted changes present. If passes → commit, mark `completed` . If fails → `git reset --hard <started_at_commit>` + `git clean -fd` , mark `failed`
Yes	Yes	Any	Commit uncommitted changes, run `validation.command` . If passes → mark `completed` . If fails → `git reset --hard <started_at_commit>` + `git clean -fd` , mark `failed`

Log recovery:

[timestamp] [SESSION-N] RECOVERY [task-id] action="<action taken>" reason="<reason>"

Error Handling & Recovery Strategies

Each error category has a default recovery strategy:

Category	Default Recovery	Agent Action
`ENV_SETUP`	Re-run init, then STOP if still failing	Run `harness-init.sh` again immediately. If fails twice, log and stop — environment is broken
`CONFIG`	STOP (requires human fix)	Log the config error precisely (file + field), then STOP. Do not guess or auto-mutate task metadata
`TASK_EXEC`	Rollback via `git reset --hard <started_at_commit>` , retry	Verify `started_at_commit` exists ( `git cat-file -t <hash>` ). If missing, mark failed at max_attempts. Otherwise reset, run `on_failure.cleanup` if defined, retry if attempts < max_attempts
`TEST_FAIL`	Rollback via `git reset --hard <started_at_commit>` , retry	Reset to `started_at_commit` , analyze test output to identify fix, retry with targeted changes
`TIMEOUT`	Kill process, execute cleanup, retry	Wrap validation with `timeout <seconds> <command>` . On timeout, run `on_failure.cleanup` , retry (consider splitting task if repeated)
`DEPENDENCY`	Skip task, mark blocked	Log which dependency failed, mark task as `failed` with dependency reason
`SESSION_TIMEOUT`	Use Context Window Recovery Protocol	New session assesses partial progress via Recovery Protocol — may result in completion or failure depending on validation

JSON corruption: If

harness-tasks.json

cannot be parsed, check for

harness-tasks.json.bak

(written before each modification). If backup exists and is valid, restore from it. If no valid backup, log

ERROR [ENV_SETUP] harness-tasks.json corrupted and unrecoverable

and STOP — task metadata (validation commands, dependencies, cleanup) cannot be reconstructed from logs alone.

Backup protocol: Before every write to

harness-tasks.json

, copy the current file to

harness-tasks.json.bak

. Write updates atomically: write JSON to

harness-tasks.json.tmp

then

mv

it into place (readers should never see a partial file).

Environment Initialization

harness-init.sh

exists in the project root, run it at every session start. The script must be idempotent.

Example

harness-init.sh

bash

#!/bin/bash
set -e
npm install 2>/dev/null || pip install -r requirements.txt 2>/dev/null || true
curl -sf http://localhost:5432 >/dev/null 2>&1 || echo "WARN: DB not reachable"
npm test -- --bail --silent 2>/dev/null || echo "WARN: Smoke test failed"
echo "Environment health check complete"

Standardized Log Format

All log entries use grep-friendly format on a single line:

[ISO-timestamp] [SESSION-N] <TYPE> [task-id]? [category]? message

[task-id]

and

[category]

are included when applicable (task-scoped entries). Session-level entries (

INIT

LOCK

STATS

) omit them.

Types:

INIT

Starting

Completed

ERROR

CHECKPOINT

ROLLBACK

RECOVERY

STATS

LOCK

WARN

Error categories:

ENV_SETUP

CONFIG

TASK_EXEC

TEST_FAIL

TIMEOUT

DEPENDENCY

SESSION_TIMEOUT

Filtering:

bash

grep "ERROR" harness-progress.txt                    # All errors
grep "ERROR" harness-progress.txt | grep "TASK_EXEC" # Execution errors only
grep "SESSION-3" harness-progress.txt                # All session 3 activity
grep "STATS" harness-progress.txt                    # All session summaries
grep "CHECKPOINT" harness-progress.txt               # All checkpoints
grep "RECOVERY" harness-progress.txt                 # All recovery actions

Session Statistics

At session end, update

harness-tasks.json

: set

last_session

to current timestamp. (Do NOT increment

session_count

here — it is incremented at Session Start.) Then append:

[timestamp] [SESSION-N] STATS tasks_total=10 completed=7 failed=1 pending=2 blocked=0 attempts_total=12 checkpoints=23

blocked

is computed at stats time: count of pending tasks whose

depends_on

includes a permanently failed task. It is not a stored status value.

Init Command (

/harness init

)

Create
```
harness-progress.txt
```
with initialization entry
Create
```
harness-tasks.json
```
with empty task list and default
```
session_config
```
Optionally create
```
harness-init.sh
```
template (chmod +x)
Ask user: add harness files to
```
.gitignore
```
?

Status Command (

/harness status

)

Read

harness-tasks.json

and

harness-progress.txt

, then display:

Task summary: count by status (completed, failed, pending, blocked).
```
blocked
```
= pending tasks whose
```
depends_on
```
includes a permanently failed task (computed, not a stored status).

Per-task one-liner:

[status] task-id: title (attempts/max_attempts)

Last 5 lines from
```
harness-progress.txt
```
Session count and last session timestamp

Does NOT acquire the lock (read-only operation).

Add Command (

/harness add

)

Append a new task to

harness-tasks.json

with auto-incremented id (

task-NNN

), status

pending

, default

max_attempts: 3

, empty

depends_on

, and no validation command (required before the task can be completed). Prompt user for optional fields:

priority

depends_on

validation.command

timeout_seconds

. Requires lock acquisition (modifies JSON).

Tool Dependencies

Requires: Bash, file read/write, git. All harness operations must be executed from the project root directory. Does NOT require: specific MCP servers, programming languages, or test frameworks.

Concurrent mode requires isolated working directories (

git worktree

or separate clones). Do not run concurrent workers in the same working tree.

harness

NPX Install

SKILL.md Content

Harness — Long-Running Agent Framework

Design Principles

Commands

Activation Marker

Progress Persistence (Dual-File System)

harness-progress.txt (Append-Only Log)

harness-tasks.json (Structured State)

Concurrency Control

Infinite Loop Protocol

Session Start (Execute Every Time)

Task Selection Algorithm

Task Execution Cycle

Stopping Conditions

Context Window Recovery Protocol

Error Handling & Recovery Strategies

Environment Initialization

Standardized Log Format

Session Statistics

Init Command (
`/harness init`
)

Status Command (
`/harness status`
)

Add Command (
`/harness add`
)

Tool Dependencies

harness

NPX Install

SKILL.md Content

Harness — Long-Running Agent Framework

Design Principles

Commands

Activation Marker

Progress Persistence (Dual-File System)

harness-progress.txt (Append-Only Log)

harness-tasks.json (Structured State)

Concurrency Control

Infinite Loop Protocol

Session Start (Execute Every Time)

Task Selection Algorithm

Task Execution Cycle

Stopping Conditions

Context Window Recovery Protocol

Error Handling & Recovery Strategies

Environment Initialization

Standardized Log Format

Session Statistics

Init Command (/harness init)

Status Command (/harness status)

Add Command (/harness add)

Tool Dependencies

Init Command (
`/harness init`
)

Status Command (
`/harness status`
)

Add Command (
`/harness add`
)