/implement

name: implement
description: 'Implement accepted behavior, repair defects or execute a selected wave with per-lane evidence. Use when: coding is authorized and ready; return facts, not a binding verdict.'
practices:
- tdd
- refactoring
- small-batch-flow
hexagonal_role: driving-adapter
consumes: []
produces:
- subject-manifest.v1
output_contract: 'content identity, author context ID and check facts through the native handoff; subject-manifest.v1 at the judgment boundary'
context_rel:
- kind: customer-of
  with: plan
skill_api_version: 1
user-invocable: true
metadata:
  graph_root: true
  tier: execution
  dependencies: []
  capabilities: [execute_one_experiment, collect_factual_evidence]
  effects: [modify_declared_subject, derive_subject_manifest]
  canonical_status: canonical
  disposition: keep

Implement

Implement the accepted outcome. Repair ordinary known defects directly. Use the existing intent; no Plan, Recall or Learn worksheet is owed for a clear edit. Implement owns source changes and factual checks; the runtime derives identity and receipts.

Workflow

1. Read intent, acceptance, scope and repository boundaries before the first write; reuse loaded contracts. RPI [boundaries](../rpi/references/boundaries.md) apply when that workflow is explicitly selected. For caller-selected episode tracking, obtain permitted work/source references and return observed runtime/context identity at startup through the native recording channel. Keep unknowns and failures explicit; invent no parentage or second tracker. The [session association reference](../cass/references/SESSION_FORMATS.md#work-to-session-associations) supplies mechanics for that selected workflow. 2. Carry the accepted behavior examples forward unchanged. Use repository domain names in symbols and tests; check observable outcomes through the relevant interface. Find actual consumers of edited paths or wording and their checks. For retirement, inspect live code, tests, schemas, instructions, installations and lookups as relevant; verify new guidance and old-name lookup behavior, preserving historical provenance. Keep exact check commands and the required integration recipe in the existing handoff. Run the smallest applicable check before and after editing. Behavioral changes preserve RED for the expected missing behavior; pure refactors, relocations or docs may have an honest green baseline. Prefer existing tests or small discriminating probes. 3. Make the smallest in-scope change. When repairing discovery or checks, preserve the consumer's existing input selection; fixing an error path does not authorize a wider scan. Use a negative control when exclusion matters. Check a representative change against existing constraints before bulk propagation; check the authored source set before broad regeneration. Repair known failures directly and verify the exact result (such as a cited file, assertion or returned record) before another review. A disproved assumption may change the approach within scope; use Plan only for consequential uncertainty. 4. Use targeted tests and applicable repository lint/static checks before broad integration. Read the repository's actual check recipe, including instrumentation and environment, rather than reconstructing it from memory. Run required full checks at integration. Reuse exact-input receipts only while source, tool and relevant environment match. Distinguish repository-mandated hook checks from discretionary repeats; neither bypass required hooks nor replay a check just to rename its receipt. A required CI job's known failure is actionable before the whole run ends. Inspect and repair it within scope; preserve the failed subject's evidence and rerun affected checks on the repair. Pending jobs do not imply success. 5. Refactor while acceptance remains green. Inspect changed tests, fixtures, goldens, tolerances, suppressions and specification text against original intent. Mocks, placeholders or weakened oracles cannot substitute for the requested behavior. 6. Have the runtime derive actual changed paths and content identity. A delegated increment awaiting integration returns an exact commit or runtime-derived content digests, author context ID and check facts in the existing handoff. The integrating caller derives `subject-manifest.v1` over the complete final subject before judgment; an independently judged increment needs its own manifest. Do not generate both merely because work was delegated. At that boundary, when changed paths affect bound acceptance evidence, run `ao provenance evidence-orphans --root <repo-root>` with one `--changed <path>` per derived path and retain its actual output. Refresh affected bindings after repairs; never invent or suppress the orphan list. 7. Return identity, check commands/results, useful failures and accessible evidence references through the native handoff, then stop. Keep full logs at their source, without duplicating inventories or status documents. Missing or truncated evidence stays explicit.

Diagnosis, scaffolding and delegated work

For an unexplained failure, first match the reported symptom and reduce the reproduction. State one causal prediction, test it with a discriminating check, and repair the cause supported by the result. Rerun the original scenario. Do not keep collecting hypotheses after the cause is understood. This compact diagnosis path is informed by [Matt Pocock's engineering skills](https://github.com/mattpocock/skills).

When scaffolding is the requested change, start from the repository's existing layout and a working vertical slice. See [scaffold references](references/scaffold/agent-facing-tool-scaffolds.md) only for the relevant tool shape. Avoid placeholder success paths and a new framework for a one-off operation.

Prefer current-session execution. If delegation is auth