feat: discussion-type issue metadata helper (idd-issue Step 3.5)

[kiki830621]

What

Adds Step 3.5: Discussion Metadata Helper to idd-issue — after an issue is created and before attachment upload, advisory-surface GitHub right-sidebar metadata (assignee / label / milestone) for discussion-type issues.

Cluster PR: closes out both feature Refs #141 and prevention Refs #142 in one change (both land in skills/idd-issue/SKILL.md).

Lean-v1 scope (per feedback_lead_minimal)

Implements the essence of Refs #141, not the full 7-component v1:

• Detection: --discussion flag is the sole primary trigger. Body-heuristic detection is opt-in behind config discussion_metadata_heuristic (design Q1's own recommended default) — standard bug/feature issues are never subjected to the 4-prompt ceremony.
• Four advisory sub-steps, all surface-only (never auto-set outward-facing metadata; unattended mode prints suggestions only, sets nothing):
  • (a) assignee from body's tagging-collaborators-verified @login set
  • (b) label = config-overridable discussion_label (default discussion)
  • (c) milestone only on a time-bound signal, reusing existing Step 4.5 machinery
  • (d) native GraphQL relationship DEFERRED (- [~], disclosed in prose)

Why (d) is deferred — not dropped

Highest complexity/risk of the four; it would reuse the v2.52.0+ --blocked-by GraphQL path, which is not yet generalized into a reusable primitive. Design Q4 already keeps the body-text #N reference regardless, so deferring loses no inline context. Light-up condition (extracting the mutation into a helper) is documented in the prose.

Folds in Refs #142 — three mandatory label safeguards

• S1 verify-by-read after gh label create (silent-succeed is indistinguishable from noop-on-exists — read-back is the only reliable detection)
• S2 pre-add existence check for the --add-label path
• S3 UI cache-sync hint at the Step 5 report, on FRESH create only — names the confusing Invalid value ... for label string + hard-refresh remedy

Tests

• New artifact-level drift-guard fixture scripts/tests/discussion-metadata/test.sh (13 assertions, TDD RED→GREEN)
• Full suite 22/22 GREEN
• Fixture locks the contract prose (trigger + 4 sub-steps + 3 safeguards + disclosed deferral) against silent deletion. It does not execute the AskUserQuestion helper — that is a Claude-runtime contract, unrunnable in a shell harness (same artifact-level pattern as session-start-commit-rule).

Merge-order note

Only references rules/tagging-collaborators.md (sub-step (a) reuses its verified-@login set) — does not modify it, so no file conflict with the #85/#86 tagging-family PRs. Independent of PR #247.

Refs #141
Refs #142

[kiki830621]

🔍 idd-verify — PR #248 (discussion-metadata helper, #141 + #142)

Verdict: ✅ PASS（round-1 修復後）

Backend（lean tier，比例原則）

此 PR 是 prose + 一個 drift-guard fixture、零可執行 runtime code（SKILL.md 內的 bash 是給 Claude runtime 遵循的指令，非測試 harness 執行）。依 #205 token-cost 裁決，全套 opus 5-agent ensemble 對此改動不成比例，故採精簡雙鏡：

• Codex 跨模型盲驗（gpt-5.5，獨立模型家族，看不到 coordinator 判斷）
• Coordinator adversarial premise-attack（攻 premise 而非 mechanics）

保留了 ensemble 最高價值的兩個 lens（cross-model blind verify + adversarial），略過同構冗餘的其餘 3 lens。

Round 1 — Codex 抓到 real defect（已修）

#	Sev	Finding	處置
1	MEDIUM	#142 S2 控制流 bug：gh issue edit --add-label 在 label_exists 的 if 之後無條件執行，註解寫「只在 verified-exist 後」但控制流沒 gate → 對不存在 label 做 --add-label 會 silently auto-create 白色 label（正是 S2 要防的 edge case）	✅ 修：把 add gate 進 if label_exists then 分支；else 導回 auto-create/skip
2	LOW	label_exists 把 $LABEL_NAME 裸插進 jq select(.name == "…") → 含引號的 custom label 名會破 jq	✅ 修：改 .[].name | grep -qx 精確比對，不插值
3	LOW	drift-guard 只 grep prose，抓不到上述控制流 bug（false-assurance 縫隙）	✅ 部分修：加 needle 鎖「不 blind add」gated 分支，把此次修復轉成 regression guard（bash 不可 shell-run，這是 artifact-level fixture 的固有上限，已誠實揭露）

修復 commit：2158b1d。

Coordinator adversarial premise-attack

• feat: discussion-type issue metadata helper — assignee / label / milestone / native relationships auto-surface #141 需求覆蓋：(a) assignee（tagging-verified @login → --add-assignee）✅、(b) label（config-overridable + bug-prevention: #141 discussion-metadata helper must verify label existence + surface UI cache-sync hint #142 S1/S2）✅、(c) milestone（time-bound gate，reuse Step 4.5）✅、(d) native relationship deferred 且 disclosed（lean 切，理由完整）✅。detection 收斂為 --discussion + config opt-in heuristic（design Q1 自身建議預設）—— lean-v1 刻意切面，非遺漏。
• bug-prevention: #141 discussion-metadata helper must verify label existence + surface UI cache-sync hint #142 safeguards：S1 verify-by-read ✅、S2 pre-add gate ✅（round-1 修好）、S3 UI cache-sync hint（Invalid value + hard refresh，gated on FRESH_LABEL_CREATED=1）✅。
• auto-close 紀律：Step 0.8 Source 1（closingIssuesReferences）clean、Source 2（per-commit trap regex，兩 commit）clean。PR body Refs #141 #142 #247 #85 #86 涵蓋兩 target issue。
• scope creep / regression：diff 只碰 2 檔（SKILL.md 純插入 + fixture），無既有內容改寫、無 unrelated 改動。

Re-verification

• drift-guard: 22 suites / 0 fail（discussion-metadata 14 needles GREEN，含新 gated-branch guard）
• CI: suites=SUCCESS、mergeState=CLEAN、mergeable=MERGEABLE

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停在 verified — 依 IDD 契約不 auto-merge、不 auto-close。人工 review → merge → /idd-close #141 #142 由你接手。