docs(archive): preserve PR #5131 discussion

docs/pr-discussions/PR-5131-rule-verify-existing-substrate-before-authoring-sibling-to-d.md

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+---
+pr_number: 5131
+title: "rule: verify-existing-substrate-before-authoring \u2014 sibling to dep-pin-search-first-authority (3-anchor empirical evidence 2026-05-26)"
+author: "AceHack"
+state: "MERGED"
+created_at: "2026-05-26T08:29:25Z"
+merged_at: "2026-05-26T08:37:39Z"
+closed_at: "2026-05-26T08:37:39Z"
+head_ref: "otto-cli/rule-ext-verify-existing-substrate-before-authoring-2026-05-26"
+base_ref: "main"
+archived_at: "2026-05-26T12:38:46Z"
+archive_tool: "tools/pr-preservation/archive-pr.ts"
+---
+
+# PR #5131: rule: verify-existing-substrate-before-authoring — sibling to dep-pin-search-first-authority (3-anchor empirical evidence 2026-05-26)
+
+## PR description
+
+## Summary
+
+Lands `.claude/rules/verify-existing-substrate-before-authoring.md` as the substrate-authoring-scope sibling to `.claude/rules/dep-pin-search-first-authority.md` (landed earlier today via PR #5126).
+
+Empirically grounded in **3 same-root-cause failures from session 2026-05-26**:
+
+- **Anchor 1**: cascade #4 ISO audit asserted training-data-default `boot/grub/grub.cfg` path (NixOS actually uses isolinux + refind). Blocked 4 ISO builds. Fixed via PR #5125. Covered by `dep-pin-search-first-authority.md`.
+- **Anchor 2**: B-0806 Ace section authored without reading `docs/agendas/ace-package-manager/AGENDA.md` + project memory + 7+ related backlog rows. The maintainer 2026-05-26: *"that is what ace has been since we first talked about it you just keep forgetting we have substantial backlog around this"*. Fixed via PR #5130.
+- **Anchor 3**: B-0806 hat/fork-negotiation NOT integrated into architecture even after Anchor 2 correction. The maintainer 2026-05-26: *"i'm assuming you have the hat / fork negoation for ace too"*. Fixed via PR #5130 follow-on commit.
+
+## Same root cause class, different surface
+
+All 3 anchors are "Otto-defaults-to-plausible-but-unverified" — at different surfaces:
+- Version pins / path assertions → covered by `dep-pin-search-first-authority.md`
+- NEW substrate authoring (backlog rows, rules, skills, agenda entries, architectural framings) → covered by THIS rule
+- Existing-rule citation as alibi for action → covered by `fighting-past-self-vs-peer-agent-distinguisher-fix-your-own-coordinate-on-peers-dont-punt-by-default.md`
+
+Together the 3 rules cover the surfaces today's empirical evidence shows are vulnerable.
+
+## Operational discipline (per the rule body)
+
+4-step pass before authoring new substrate:
+1. Grep across substrate surfaces (agendas + trajectories + backlog + rules + memory + research)
+2. READ THE TOP HITS (not just list them)
+3. Decide: existing-covers / partial / no-existing
+4. Cite the search inline in the new substrate
+
+Auto-loads at cold-boot per wake-time-substrate.
+
+## Test plan
+
+- [x] Single rule file added; no other surface modified
+- [x] Cross-references to dep-pin + fighting-past-self + skill-router + grep-substrate-anchors compose cleanly
+- [x] 3 empirical anchors preserved with verbatim maintainer quotes
+
+🤖 Generated with [Claude Code](https://claude.com/claude-code)
+
+## Reviews
+
+### COMMENTED — @copilot-pull-request-reviewer (2026-05-26T08:32:15Z)
+
+## Pull request overview
+
+Adds a new `.claude/rules/` wake-time substrate rule that formalizes a “search and read existing substrate before authoring new substrate” discipline, positioned as the substrate-authoring counterpart to `dep-pin-search-first-authority.md`.
+
+**Changes:**
+- Introduces `verify-existing-substrate-before-authoring.md` with a required pre-authoring inventory/search process and an inline checklist template.
+- Captures three empirical anchors from 2026-05-26 to justify the rule and keep the motivating evidence present at cold-boot.
+- Cross-references existing related rules to clarify composition across surfaces (dep pins, rule-citation failures, substrate authoring).
+
+## Review threads
+
+### Thread 1: .claude/rules/verify-existing-substrate-before-authoring.md:38 (resolved)
+
+**@copilot-pull-request-reviewer** (2026-05-26T08:32:14Z):
+
+The “Grep for the topic across substrate surfaces” snippet doesn’t actually grep agenda/trajectory *content* (it only filters directory names), and it also omits `.claude/skills/` even though skills are in-scope later in this rule. Consider switching to a content search over the authoritative files (e.g., `AGENDA.md`, trajectory `RESUME.md`, backlog markdown, rules, skills) so the inventory pass can’t miss substrate just because the directory/filename doesn’t contain the keyword.
+
+### Thread 2: .claude/rules/verify-existing-substrate-before-authoring.md:38 (resolved)
+
+**@copilot-pull-request-reviewer** (2026-05-26T08:32:14Z):
+
+The search commands treat `topic` as a regex (`grep -E` / `grep -i`) and also use unquoted glob expansion (`memory/*${topic}*`), which can produce wrong matches or break when the topic contains regex metacharacters or spaces. If the intent is a literal keyword search, use fixed-string matching and a safer approach than `ls`+globs for hits (so the recommended process is reliable across topics).
+
+### Thread 3: .claude/rules/verify-existing-substrate-before-authoring.md:162 (resolved)
+
+**@copilot-pull-request-reviewer** (2026-05-26T08:32:15Z):
+
+The markdown table under “The composition with dep-pin-search-first-authority” uses double leading pipes (`||`), which will render as an unintended empty first column in GitHub Markdown. Use standard table syntax with single leading pipes so the table displays with the intended two columns.
+
+## General comments
+
+### @chatgpt-codex-connector (2026-05-26T08:29:31Z)
+
+You have reached your Codex usage limits for code reviews. You can see your limits in the [Codex usage dashboard](https://chatgpt.com/codex/cloud/settings/usage).