Apply after any non-trivial implementation task — evaluates whether an ADR is warranted, writes to Atelier-ADR repo when yes, names the skip reason when no, and generates E2E tests for every new structural invariant so LDD has a loss signal. High bar: most tasks produce no ADR.
Loss-Driven Development (LDD) — Gradient Descent for Agents. Use whenever the user prefixes a message with 'LDD:' or mentions LDD, loss, gradient, SGD on code, drift, refinement loop, outer loop, inner loop, method evolution, or 'apply LDD'. Dispatcher for 14 sub-skills (reproducibility-first, root-cause-by-layer, loss-backprop-lens, e2e-driven-iteration, loop-driven-engineering, iterative-refinement, method-evolution, drift-detection, dialectical-cot, dialectical-reasoning, docs-as-definition-of-done, define-metric, architect-mode, bootstrap-userspace) loaded on demand from references/. Also triggers on: failing test, bug, error, flaky, symptom patch, design, architect, greenfield, refactor, polish, declaring done, ready to merge, release candidate, drift check.
Use at the start of any LDD session running under Claude Code — auto-installs a permanent statusline that shows the current LDD task, loop, iteration, loss, and a Unicode loss-curve sparkline at all times, without any user action or configuration. Idempotent, merge-safe, project-local. Silently no-ops on non-Claude-Code hosts. Fires once per session in parallel with `bootstrap-userspace`.
Use whenever the user prefixes a message with "LDD:" or mentions LDD, loss-driven development, loss, gradient, SGD on code, drift, refinement loop, outer loop, inner loop, method evolution, or "apply LDD". Bootstrap / entry-point skill that explains how to dispatch the other LDD skills and the trigger-phrase table they respond to.
The 5-phase design protocol that is active at thinking-levels L3 and L4. NOT a separate mode — it is the discipline the level preset pulls in. Opt-in via four paths — inline `LDD[level=L3]:` (or `LDD[level=L4]:`) prefix, the `/ldd-architect` command, trigger phrases like "design" / "architect" / "from scratch" / "greenfield", or the thinking-levels auto-dispatch landing at L3 / L4 (9-signal scorer; see `../using-ldd/SKILL.md` § Auto-dispatch: thinking-levels). Supports three creativity levels (`conservative` | `standard` | `inventive`) that change the loss function, not the amount of structure.
Use at the start of any LDD task when there is no existing `.ldd/trace.log` readable in the working directory — fires before any other LDD skill writes trace state. Detects the host's persistence capabilities (filesystem, artifact/canvas, conversation-history, memory-pointer, inline-only), picks the most durable tier silently without prompting the user, restores any prior trace state it finds, and announces the chosen store in the LDD trace block's `Store :` header line. Makes LDD portable across Claude Code, Claude Desktop, Codex, Gemini CLI, Cursor, ChatGPT, and any other host the LLM can introspect.
Use when the agent or the user wants to introduce a new measurable quantity as a first-class loss component — e.g., tracking cyclomatic complexity alongside test_pass_rate, or adding a domain-specific rubric to a reasoning chain. Forbids ad-hoc arithmetic on observations and forbids using a new metric as a load-bearing decision gate until calibration has passed. Extends LDD's loss framework to agent-defined objectives without touching LDD core.
Use at the start of any non-trivial engineering task (feature, bugfix touching more than one file, refactor with observable behavior change, incident response). Orchestrates LDD's four loops — inner (code), refinement (deliverable), outer (method), CoT (reasoning chain, v0.8.0) — with hard iteration budgets, dispatches the specialist skills at the right moments, and forbids declaring "done" without a synced doc-level mental model.