Harness Engineering · Episode 06

Your Monday Morning Harness Kit

Nine days to diagnose. Twelve weeks to ship.

Arc · The practice Episode · 6 of 8 Next · Episode 07 — Organizations That Rebuilt Around Agents
After this you will know
  • InspectHow to examine the agent system you already have.
  • ReadWhich production evidence to read before proposing architecture.
  • PlaceHow to put your team on a five-rung maturity ladder.
  • FileThe four tickets that start a feedback loop.
  • TranslateThe same work explained for engineering, design, leadership, and security.

01The first five episodes, compressed

Episode 1 taught us to find the first point where a run diverged from the user's intended outcome.

Episode 2 gave us the map: Model, Harness, Tools, Environment, with five decisions inside the harness.

Episode 3 showed four small interventions: useful retry feedback, structured output, a narrow tool surface, and external completion evidence.

Episode 4 turned those interventions into tensions. Every constraint can help and every workaround can expire.

Episode 5 priced the system. The useful unit is cost per acceptable completed workflow, not cost per token.

This episode puts all five into one operating plan.

02Monday, 9:04 AM

The reconciliation team agrees that the current system needs work.

Nobody has approved a platform migration, a new team, or a six-month transformation program.

Good. Week one should begin with evidence, not architecture.

For nine working days, the team will inspect what already exists, read how it fails, and turn the findings into four tickets. The next twelve weeks will ship those changes one decision at a time.

Days 1 to 9 diagnose. The twelve weeks ship.

Choose one workflow before you begin. Pick the one that creates recurring operational pain, not the one that looks best in a demo.

The invoice workflow qualifies because incomplete runs trigger a 2 AM page, require manual reconciliation, and create a clear business outcome the team can verify.

Figure 01 · Concept
Nine days diagnose. Twelve weeks ship.
EVIDENCE BEFORE ARCHITECTURE DAYS 1–9 · DIAGNOSE Read what is true Map · sessions · interviews Tools · eval gap · maturity Tickets · evals · ownership 7 ARTIFACTS WEEKS 1–12 · SHIP One decision at a time Identity · memory · tools · observability Orchestration · interception · portability Feedback · second model · discipline WHAT CROSSES THE LINE 01 System map with owners 02 Failure tally 03 Operator workarounds 04 Tool decision table 05 Eval-debt list 06 Maturity diagnosis 07 Four owned tickets — the only thing that reaches the backlog If you are holding a platform proposal instead, you moved too early.
Read it as The short lane buys the right to use the long one. Nine days of evidence decide which twelve weeks are worth spending.

03What this kit produces

At the end of nine days, you should hold seven artifacts:

  1. A map of the current system
  2. A tally of production failure shapes
  3. A list of operator workarounds
  4. A tool decision table
  5. An eval-debt list
  6. One maturity diagnosis
  7. Four owned tickets

If you are holding a platform proposal instead, you moved too early.

04Days 1 to 3 — map, read, interview

Day 1 Map what already exists

QuestionWhat system is production running today?

Most teams already have a harness. They do not call it one.

The prompt lives in one repository. Retry logic sits in a utility. Tool permissions come from an API gateway. Traces land in an observability platform. A spreadsheet holds the eval cases. Three people own fragments and nobody owns the behavior produced by the whole.

Draw one page with four columns — Model, Harness, Tools, Environment — and add Runtime beneath them.

Inside Harness, add five rows: Identity, Memory Policy, Orchestration, Interception, Observability and Evals.

For each row, record:

FieldQuestion
ImplementationWhere does this job happen?
OwnerWho can change it?
EvidenceHow do we know it works?
FailureWhat does a defect look like?

Write “missing” when no implementation or owner exists. Do not fix anything today.

ArtifactOne system map with owners and missing rows. ConnectionThe anatomy from Inside a Production Agent Harness (Episode 02) applied to your code and vendors.
Day 2 Read fifty complete sessions

QuestionHow does the workflow fail in real use?

Read sessions, not final responses.

A session includes the request, context, tool calls, retries, state changes, and final outcome. The final answer can look correct while the path contains wasted loops, unsafe calls, or unverified effects.

Tag the six failure shapes from Episode 1:

Failure shapeWhat to look for
Premature stopWork remains after a clean exit
Infinite loopRepeated action without new evidence
Silent driftCorrect-looking work against stale intent
Vocabulary mismatchSame term used with different business meanings
Unauthorized actionAction exceeds the user's or agent's authority
Worker divergenceParallel results conflict or lose work during merge

For each failed session, mark the intended business outcome, the observed outcome, the earliest divergence, the layer that owned the preventable condition, and the evidence available.

Do not begin with an existing taxonomy beyond the six broad shapes. Read several traces first. New failure patterns may not fit your current labels.

ArtifactA failure tally plus three representative sessions the whole team can inspect. ConnectionEpisode 1 supplied the diagnostic questions. Day 2 applies them to your traffic.
Day 3 Interview the people who repair the system

QuestionWhat does the organization quietly work around?

Speak separately with the staff engineer and the person who takes the page. Ask two questions:

  1. What do you repair manually without filing anymore?
  2. If feature work stopped for one sprint, what would you fix first?

The first question surfaces hidden operating cost. The second surfaces accumulated judgment.

Listen for manual restarts, hand-corrected state, secret spreadsheets, prompt edits applied during incidents, repeated tool overrides, cases reviewers always reverse, and alerts everyone ignores.

The overlap between both interviews is often the first high-confidence ticket.

ArtifactTwo short lists and an overlap section. ConnectionEpisode 5 priced senior attention and human review. Day 3 finds where that cost is already being paid invisibly.

05Days 4 to 6 — tools, evals, maturity

Day 4 Audit the tool surface

QuestionWhich tools create useful action, and which create confusion or risk?

Pull the current tool registry. Score each tool on four dimensions.

DimensionQuestion
UsageHow often is it selected?
ContributionDoes it help complete the task?
OverlapDoes another tool perform the same job?
ConsequenceWhat happens if it is selected incorrectly?

Then make one decision per tool: keep visible, rename, tighten the input contract, hide behind a skill, require approval, merge, or remove.

Do not delete the bottom third automatically. A rare escalation tool may be essential. A frequently used general tool may be the source of repeated errors.

Add two ownership fields: which identity calls the tool, and which team owns its permission and verification policy.

Detailed authority, reversibility, and protocol design belongs in The Tool Is the Contract. This audit needs the decision, not a protocol migration project.

ArtifactTool decision table with owner and side-effect class. ConnectionEpisode 3 taught the narrow decision surface. Day 4 finds whether your catalogue is narrow, clear, and properly bounded.
Day 5 Find the eval gap

QuestionWhich promised behavior can break without any test failing?

List the behaviors the product claims to support. For invoice reconciliation:

  • MatchFull payments correctly
  • PartialHandle partial payments
  • DuplicateFlag duplicates
  • ScopeStay inside tenant scope
  • ExceptionAssign every exception
  • QueueProcess the full eligible queue

For each behavior, ask:

If this broke tomorrow, which automated check would fail?

A blank answer is eval debt. Put one class at the top when it exists: we have no machine-checkable definition of done for the workflow.

Without that definition, every other eval measures pieces while the agent can still stop with the job unfinished.

Evaluate at the right altitude

Current agent-evaluation practice separates three levels:

LevelWhat it checksInvoice example
RunOne model or tool stepDid it choose the correct invoice tool?
TraceOne complete agent turnDid the full reconciliation action succeed?
ThreadMulti-turn or multi-session outcomeDid it finish the user's goal across the whole interaction?

A final-answer eval can miss a bad path. A run-level check can pass while the whole conversation fails.

ArtifactBehavior-to-eval table with blank rows highlighted. ConnectionEpisode 3 separated syntax, meaning, and completion. Day 5 checks coverage at all three levels.
Day 6 Write the maturity diagnosis

QuestionWhat problem is the team equipped to solve next?

Use five rungs.

RungEvidence
1: PromptOne model call; little durable state or traceability
2: RetryParsing and retries exist; behavioral measurement is thin
3: Eval suiteGround truth and regression checks run before changes ship
4: HarnessAll five control-plane jobs have implementations and owners
5: DisciplineVersions, migrations, trace-to-eval loop, and retirement practice run on cadence

Do not average the whole organization into one score. Place the selected workflow. Write one paragraph:

We are at Rung [N] because [evidence]. The next rung requires [capability]. The smallest move is [ticket]. We will know it worked when [metric].

The reconciliation workflow is at Rung 2. We trace model calls but have no ground-truth test for full-queue completion. The next rung requires a workflow eval in CI. The smallest move is Ticket 2. We will know it worked when a pagination regression fails before release.

ArtifactOne paragraph, read aloud to engineering. ConnectionEpisode 4 taught conditional decisions. The maturity paragraph states the condition for moving.

06Days 7 to 9 — tickets, onboarding, ownership

Day 7 Write four tickets

QuestionWhich changes are small enough to own and specific enough to measure?

The audit should compress into four tickets:

  1. Enforce a structured contract on the highest-volume model output.
  2. Add a ground-truth eval for the highest-consequence journey.
  3. Trace the call the on-call team cannot explain.
  4. Complete one trace-to-eval-to-change cycle.

Each ticket needs a named owner, one workflow, a baseline, acceptance criteria, a counter-metric, and a rollout and rollback plan.

ArtifactFour tickets in the real backlog, not a strategy deck.
Day 8 Onboard evals

QuestionCan the team turn production evidence into a release decision?

LangChain's 2026 survey found that 89% of respondents had some agent observability, while 52.4% ran offline evaluations on test sets and 37.3% ran online evaluations. Many teams can watch a run without converting what they see into a test.

Start smaller than your ambition.

  1. Manually review 20 to 50 real traces with a domain expert.
  2. Define success for one task.
  3. Write five eval cases from Day 5's gaps.
  4. Run them against the current system and record the baseline.
  5. Put one regression eval in CI.
  6. Attach feedback to the trace or thread it judges.

A trace tells you what happened. Feedback records what that behavior meant.

Calibrate judgment without a magic threshold

Some properties can be checked with code: required field, date range, source count, permission.

Semantic properties may need a model judge or human: whether the response resolved the user's intent, followed brand tone, or chose a reasonable path.

Calibrate model judges on labeled examples from this workflow. Prefer clear binary or categorical decisions. Review disagreements. Keep human judgment on consequential cases. Recalibrate when the agent, rubric, model judge, or traffic changes.

There is no universal sample size or agreement percentage that makes a judge safe for every workflow.

ArtifactFive evals, one baseline, one CI gate, and a named eval owner. ConnectionEpisode 5 funded ground truth. Day 8 puts the first version into operation.
Day 9 Audit what you own

QuestionWhich product judgment remains portable if a vendor changes or disappears?

Run the question across five clusters.

ClusterOwnership question
IdentityCan we export and version prompts, role, and operating rules?
Memory PolicyCan we inspect context assembly, retrieval, and compaction?
OrchestrationCan we change models or runtimes without rewriting the workflow?
InterceptionCan we control approval and policy checkpoints?
Observability and EvalsCan we export traces, datasets, rubrics, and results?

Score each as owned and portable, configurable but vendor-dependent, or locked inside the product.

Add two continuity rows: has the fallback model passed the same workflow eval, and can the runtime export enough state to resume or migrate unfinished work?

A closed system may be correct for a commodity workflow. The audit prevents the decision from happening by accident.

Environment containment and reach need a separate operate-side audit. The World Around the Agent provides that method. Day 9 only records who owns the boundary and where the evidence lives.

ArtifactPortability table with one accepted dependency and one risk to reduce. ConnectionEpisode 5's rule was rent operations, own meaning. Day 9 shows whether that is true.

07The four tickets

Ticket 1
Enforce a structured contract

Drift enters a high-volume boundary repeatedly.

  • Define required fields and allowed values.
  • Reject unagreed fields.
  • Add semantic checks after parsing.
  • Version the contract.
  • Define the experience when no valid result exists.
  • Roll out behind a flag.
Target
The highest-volume model output consumed by another system.
Done when
Schema failures fall, semantic correctness holds, and empty or refused outcomes remain within the agreed threshold.
Economic variable
Successful completion rate and recovery cost.
Counter-metric
Empty-result and escalation rate.
Ticket 2
Add a ground-truth workflow eval

The team discovers regressions through users or on-call.

  • Select representative successful, borderline, and failed cases.
  • Record the approved outcome and evidence.
  • Include at least one full-workflow completion check.
  • Run against the current version.
  • Add a regression gate to CI.
Target
The journey whose failure creates the largest business consequence.
Done when
A known production failure reliably fails before release and the baseline is visible.
Economic variable
Consequential failure rate and expected failure loss.
Counter-metric
False blocks on acceptable behavior.
Ticket 3
Trace the unexplained call

Repair time is being paid through senior attention.

  • Add a trace ID.
  • Record redacted context with source provenance.
  • Record model, prompt, tool, and policy versions.
  • Record normalized tool arguments and authorization decisions.
  • Record retries, state changes, latency, and completion evidence.
  • Put sensitive payloads under tighter access and retention.
Target
The call that reaches on-call without enough evidence to diagnose.
Done when
On-call can identify the first divergence inside an agreed time and one open incident closes using the trace.
Economic variable
Diagnosis and recovery cost.
Counter-metric
Storage cost and sensitive-data exposure.
Ticket 4
Complete one feedback cycle

Traces and evals exist but do not yet change the system.

  1. Label the failure precisely.
  2. Add representative cases.
  3. Split cases used to design the change from holdout cases used only to validate it.
  4. Make one harness change.
  5. Test the change and counter-metrics.
  6. Review second-order effects.
  7. Ship with version and rollback.
  8. Write a one-page record of what changed and why.
Target
The most frequent or consequential failure found on Day 8.
Done when
One failure moved from production trace to regression test to validated change.
Economic variable
Time from failure to prevention.
Counter-metric
Regression in another behavior class.
Figure 02 · Practice
Four tickets on the map
EVERY TICKET NAMES A FAILURE, A LAYER, A METRIC, AND AN OWNER TICKET HARNESS CLUSTER ECONOMIC VARIABLE OWNER 01 Structured contract Highest-volume output boundary Interception Completion rate, recovery cost Counter: empty-result rate Product 02 Ground-truth eval Highest-consequence journey Observability and evals Expected failure loss Counter: false blocks Eval owner 03 Trace coverage The call on-call cannot explain Memory policy and runtime Diagnosis and recovery cost Counter: storage and exposure Platform 04 Feedback cycle The failure found on Day 8 Identity and orchestration Time from failure to prevention Counter: regression elsewhere Whole team See it, judge it, prove it, compound it. That is the order.
Read it as A ticket without a cluster is a wish. A ticket without an economic variable cannot be argued for at the next planning meeting.

08Why these four come first

Each ticket closes a different gap from the first five episodes.

TicketEpisode connectionWhat it changes
Structured contractEpisode 3Narrows invalid output
Ground-truth evalEpisodes 1 and 5Defines good and prices failure
Trace coverageEpisode 2Makes the lifecycle visible
Feedback cycleEpisodes 3 and 8Makes learning repeatable

The order is deliberate.

A team cannot improve a failure it cannot see. It cannot judge a trace without ground truth. It cannot prove a change without an eval. It cannot compound until the result returns to the release loop.

09The twelve-week runway

The nine days produce the diagnosis. The next twelve weeks spread implementation so each change remains attributable.

WeekFocusOutput
1IdentityInventory and version prompts and operating rules
2Memory PolicyMeasure what enters, leaves, and survives context
3ToolsRename, narrow, and classify tool consequences
4ObservabilityFirst trace set, baseline, and CI eval
5OrchestrationRoute by task difficulty and test the routing rule
6InterceptionAdd one approval, validation, or completion checkpoint
7Memory PolicyReveal tools and context only when needed
8PortabilityComplete the ownership audit and fallback model test
9FeedbackPromote one failed trace into the eval set
10IdentityReplace one vague rule with a specific example or boundary
11ModelRun the workflow suite on a second model
12DisciplineComplete and review one full feedback cycle

Do not run the calendar mechanically. If Day 6 shows the workflow lacks trace coverage, Week 4 moves earlier. The sequence is a default, not a substitute for the diagnosis.

10The stakeholder translations

The work is the same. The reason each stakeholder should care is different.

Engineering
We already have a harness. It grew across prompts, utilities, APIs, and manual workarounds. The audit makes it visible. These four tickets reduce the failures on-call currently diagnoses from scratch.
Design
Users experience the harness as consistency. State, retries, completion rules, and refusal behavior decide whether the same request feels dependable or arbitrary. The tickets target the places where trust breaks.
Leadership and finance
The investment lowers expected failure cost and creates evidence for wider delegation. We will track validated completion, review load, recovery time, and the gate for expanding this workflow.
Security and compliance
The system needs an attributable record of context sources, tool requests, authority decisions, and effects. The audit identifies which controls are enforceable and which exist only as instructions.

The translation should not change the plan. If each stakeholder hears a different project, alignment will disappear during delivery.

11Connecting the dots

This kit is a product-discovery process for a stochastic system.

Traditional discovery asks what users need and whether the product creates value. Harness discovery adds another question: which invisible decision prevents that value from surviving production?

The nine days follow the same logic as the whole season:

That is why the kit begins with traces rather than technology selection. A platform can help only after the team knows which decisions it needs the platform to own.

The audit will also expose an organizational problem. Several rows will have implementations but no clear owner. Episode 7 is about that hole.

12In practice: the one-page output

At the end of Day 9, publish one page:

SectionContent
WorkflowOne sentence defining the business outcome
Current rungEvidence-based maturity diagnosis
Top failuresThree shapes with representative traces
Missing decisionsClusters or boundaries with no implementation or owner
Four ticketsOwner, metric, counter-metric, target sprint
Economic gateEvidence required to expand volume or autonomy
Portability riskOne accepted dependency and one risk to reduce

Take that page to sprint planning. Do not take a 40-slide transformation deck.

The kit produces owners as often as it produces code changes. The same prompt may be edited by product, the retry loop owned by engineering, tool permission set by platform, and eval threshold decided in a spreadsheet no team officially owns.

You now hold
Practice 06 A nine-day diagnostic, seven artifacts, a five-rung placement, four owned tickets, and a twelve-week runway that keeps every change attributable.
The next question
Who has decision rights over the behavior produced by all four layers?
Continue
Harness 07 Organizations That Rebuilt Around Agents — being republished from the definitive draft; the season map is live on the hub.
Read alongside
Environment 00 The World Around the Agent — the operate-side audit Day 9 deliberately leaves out.
Sources
  1. LangChain — State of Agent Engineering: observability adoption alongside offline and online evaluation rates.
    langchain.com/state-of-agent-engineering
  2. LangChain — Agent Evaluation Readiness Checklist.
    langchain.com/blog/agent-evaluation-readiness-checklist
  3. LangChain — Evaluating AI agents at the run, trace, and thread level.
    langchain.com/resources/agent-evals
  4. LangChain — Agent observability needs feedback to power learning.
    langchain.com/blog/agent-observability-needs-feedback-to-power-learning