feat(opencode): skill parity — generate the tree from canonical ctx skills

[omergk28]

feat(opencode): skill parity — generate the tree from canonical ctx skills

Branch: feat/158-opencode-skill-parity → main · Closes #158
Commits: f0176142, f3f73875, 13fe9304 · Spec: specs/opencode-skill-parity.md

What

Aligns OpenCode with the Copilot CLI model: the skill tree is
generated from internal/assets/claude/skills/ at build time.

• hack/sync-opencode-skills.sh — sibling of the Copilot script,
  same contract: opt-in by directory presence, allowed-tools:
  frontmatter strip, OpenCode-only skills untouched. shellcheck-clean.
• Makefile: sync-opencode-skills runs in make build;
  check-opencode-skills gates make audit (fails on staleness and
  restores state, mirroring the Copilot gate).
• 17 skills enrolled: the existing 10 (terse hand-written variants
  replaced by canonical bodies) + the Design Before Coding planning
  arc (ctx-brainstorm, ctx-plan, ctx-spec, ctx-task-out,
  ctx-implement) + capture pair (ctx-task-add,
  ctx-decision-add). Canonical names, 1:1 with the Claude tree.
• New test TestSyncedSkillParity
  (internal/assets/read/skill/parity_test.go): asserts every
  synced skill in BOTH generated trees (OpenCode + Copilot CLI) is
  byte-identical to its Claude source minus allowed-tools: lines.
  This moves the sync contract into go test, so CI now enforces
  it — previously only make audit on developer machines did.
  Verifies 52 synced skills, 14 Copilot tool-only exempt.
• Zero Go source changes: embed glob, agent.OpenCodeSkills(), and
  deploySkills() already walk whatever directories exist.
• Docs: docs/home/opencode.md slash-command section lists the full
  synced set (relative recipe link per docs conventions); site/
  regenerated for that page + search.json only (see below).

Verification

• make audit fully green (run on main + this + the sibling
  hack-portability fix, i.e. post-merge state), including the new
  check-opencode-skills gate.
• Byte-parity of all 17 skills verified against the sed transform.
• Staleness path verified: deliberately staled a skill →
  check-opencode-skills fails and restores state.
• End-to-end smoke: built binary, ctx setup opencode --write in a
  fresh temp repo → all 17 skills deployed, deployed content
  byte-identical to embedded source.
• TestSkillFrontmatter covers the 7 new dirs automatically.

Decisions / notes for review

• No terse transform (issue's open question): the hand-written
  terseness was truncated reference material, so canonical bodies
  replace it. This also drops a couple of genuinely OpenCode-specific
  lines (e.g. ctx-status's "slash command takes no arguments" note) —
  judged not worth a divergent transform; revisit in the sync script
  if OpenCode-specific adaptation is ever needed.
• site/ regen scoped to the opencode page + search.json: a full
  make site with the exactly-pinned zensical 0.0.51 churns 100+
  unrelated pages with HTML-entity encoding differences (underlying
  library drift; captured as a LEARNING). Excluded to keep the PR
  isolated.
• Sibling PR fix/hack-script-portability should merge first so
  make audit runs for macOS reviewers; this PR does not depend on
  it for CI.