What happened?

implement-issue's legacy plan-comment locator (.claude/skills/implement-issue/SKILL.md §"Step 2 —
Read the plan", and the duplicated recipe in references/github-mechanics.md §2) has a fallback branch
for issues whose plan comment lacks the 🛠️ Implementation plan marker: it re-searches for the latest
comment containing - [ ]/- [x] checkbox lines instead. That fallback is guarded by:

PLAN_COMMENT_ID=$(gh api "repos/{owner}/{repo}/issues/$ISSUE/comments" --paginate --slurp \
  | jq -r '[.[][] | select(.body | contains("🛠️ Implementation plan"))] | last | .id')

# Fallback if no marker (older/hand-written plan): latest comment that has checkbox lines.
if [ -z "$PLAN_COMMENT_ID" ]; then
  PLAN_COMMENT_ID=$(gh api "repos/{owner}/{repo}/issues/$ISSUE/comments" --paginate --slurp \
    | jq -r '[.[][] | select(.body | (contains("- [ ]") or contains("- [x]")))] | last | .id')
fi

When the primary select(...) | last | .id filter matches nothing, last on an empty array is JSON
null, and null | .id is also null. Both jq -r and gh api --jq print a null result as the
literal 4-character string null, not an empty string — confirmed locally: echo '{}' | jq -r '.foo' prints null. So PLAN_COMMENT_ID is assigned the string "null", and [ -z "$PLAN_COMMENT_ID" ] is false (the string is non-empty) — the fallback branch is dead code, and the same problem
recurs one line later at [ -z "$PLAN_COMMENT_ID" ] && { echo "No implementation plan…"; exit 1; },
which also never fires on a genuine no-match. Instead the flow falls through to gh api "repos/{owner}/{repo}/issues/comments/null" --jq .body, a REST call against the literal path segment
null, which 404s with a confusing HTTP 404: Not Found rather than either finding the right comment
or a clear "no plan" message.

Discovered while implementing #1544 (a sibling bug in the same lines — --paginate --jq not
merging pages before filtering — fixed in PR #1550), but left alone there since it's a distinct bug
class (an emptiness check, not a pagination-merge bug) and #1544 explicitly scoped itself to "do not
re-audit unrelated --paginate call sites in this PR."

Minimal .koi model

N/A — this is a bug in a .claude/skills/implement-issue shell recipe (agent tooling), not the Koine
compiler, emitter, or a .koi model.

Steps to reproduce

1. Pick (or seed) a GitHub issue whose comments contain no 🛠️ Implementation plan marker and
   no - [ ]/- [x] checkbox lines at all (e.g. a plain issue with only prose comments).
2. Run the primary locator from github-mechanics.md §2 against it:

   gh api "repos/{owner}/{repo}/issues/<ISSUE>/comments" --paginate --slurp \
     | jq -r '[.[][] | select(.body | contains("🛠️ Implementation plan"))] | last | .id'

3. Observe the output is the literal text null, not an empty string.
4. Trace that value through [ -z "$PLAN_COMMENT_ID" ] — the test is false, so the fallback search
   (checkbox-comment lookup) and the final "no plan, exit 1" guard are both skipped, and execution
   proceeds to fetch comment id null.

Actual output / error

$ echo '{}' | jq -r '.foo'
null
$ [ -z "null" ] && echo EMPTY || echo NOT-EMPTY
NOT-EMPTY

Expected: the emptiness checks should also treat the literal string null as "not found," so the
fallback search and the final stop-with-a-clear-message branch actually run.

Koine version

N/A — no koine CLI/compiler version is implicated. Repro is against .claude/skills/implement-issue
at main@73ed1568 (post PR #1550).

Environment

N/A — pure gh/jq/bash shell-recipe bug in an agent skill, reproducible on any platform with gh
and jq installed (verified with jq-1.7.1, gh per gh --version in this environment).

Related: #1544 (root cause discovered while implementing its fix), PR #1550 (fixed the sibling
pagination-merge bug in the same lines).

# Primary marker search — append `// empty` so "no match" is a true empty string, not the text "null".
PLAN_COMMENT_ID=$(gh api "repos/{owner}/{repo}/issues/$ISSUE/comments" --paginate --slurp \
  | jq -r '[.[][] | select(.body | contains("🛠️ Implementation plan"))] | last | .id // empty')

# Fallback if no marker (older/hand-written plan): latest comment that has checkbox lines.
if [ -z "$PLAN_COMMENT_ID" ]; then
  PLAN_COMMENT_ID=$(gh api "repos/{owner}/{repo}/issues/$ISSUE/comments" --paginate --slurp \
    | jq -r '[.[][] | select(.body | (contains("- [ ]") or contains("- [x]")))] | last | .id // empty')
fi

# Nothing in the body AND nothing in comments? Stop — there is no plan to execute (Autonomy contract).
[ -z "$PLAN_COMMENT_ID" ] && { echo "No implementation plan on #$ISSUE"; exit 1; }

🛠️ Implementation plan

For agentic workers: REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (- [ ]) syntax for tracking.

Goal. Fix implement-issue's legacy plan-comment locator so a genuine "no plan comment" case is
correctly detected (fallback search runs, then the stop-guard fires) instead of silently falling
through to a REST call against the literal comment id null.

Architecture / Tech Stack. Markdown skill definitions under .claude/skills/implement-issue/ plus
gh / gh api / jq shell recipes. No compiler, emitter, or workflow YAML is touched.

Global Constraints.

• Commit identity: git -c user.email=phmatray@gmail.com -c user.name="Philippe Matray".
• PR title: Conventional Commits, e.g. fix(skills): …; end with (#<issue>). pr-title-lint.yml enforces this.
• Scope: only references/github-mechanics.md §2's two jq filters and their .id output — do not
  touch the --paginate --slurp pagination-merge shape fix(skills): implement-issue's plan-comment lookup can corrupt its id across paginated comments #1544/PR fix(skills): flatten paginated comments before selecting the latest plan comment (#1544) #1550 already fixed, and do not re-audit
  other --paginate call sites (merge-pr's check-runs recipe is a different filter shape and is not
  affected by this bug).

Task 1: Make null-vs-empty detection correct in the plan-comment fallback

Files: modify .claude/skills/implement-issue/references/github-mechanics.md (§2 locator, both
jq filters and their surrounding prose).

Interfaces: the documented recipe — ... | last | .id // empty piped from gh api --paginate --slurp.

• Step 1: In references/github-mechanics.md §2, append // empty to the primary marker
  search's jq filter (... | last | .id → ... | last | .id // empty).
• Step 2: Append the same // empty to the checkbox-fallback search's jq filter.
• Step 3: Update the prose immediately below the code block to note why // empty is required
  (jq/gh api --jq prints the literal string null for a JSON null result, which the existing
  -z checks don't treat as empty).
• Step 4: Verify by hand: run both filters against a seeded empty-match JSON array and confirm
  output is truly empty (jq -r '... | last | .id // empty' <<< '[]' prints nothing), and against a
  seeded matching array to confirm a real id still prints unaffected. Paste the verification into the
  PR description.
• Step 5: Commit: fix(skills): treat a null jq match as empty in the plan-comment fallback.