docs(ultraplan-local): remove ultra-cc-architect references (SC-6 doc-rydding)

Step 12 of v3.4.1 plan. Surgical line-by-line generalization of references
to the ultra-cc-architect plugin (no longer publicly distributed):

- CLAUDE.md: 8 hits → "opt-in upstream architect plugin (not bundled)"
- README.md: 9 hits including bare slug at line 646 (removed entirely);
  rephrased to "no longer publicly distributed" with the architecture/
  filesystem slot still supported by /ultraplan-local
- SECURITY.md: 1 hit → generalized "Opt-in upstream architect step"

CHANGELOG.md historical references preserved per brief; appended a
2026-05-04 note at top of [3.0.0] block stating the plugin is no longer
publicly distributed but the architecture/overview.md slot remains
supported for any compatible producer.

The architecture/overview.md filesystem contract (Handover 3, EXTERNAL,
drift-WARN) is unchanged — anyone implementing a compatible producer
can plug in.

361 tests still green (no regressions). doc-consistency pins for
/ultracontinue-local and Handover 7 § Lifecycle still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/ultraplan-local/CLAUDE.md

@@ -4,7 +4,7 @@ Deep implementation planning and research with an explicit brief step, specializ
 
 **Design principle: Context Engineering** — build the right context by orchestrating specialized agents. Each step in the pipeline (brief → research → plan → execute) produces a structured artifact that the next step consumes.
 
-> **v3.0.0 — architect extracted to separate plugin.** `/ultra-cc-architect-local` and `/ultra-skill-author-local` were moved to the `ultra-cc-architect` plugin (v0.1.0). The plan command still auto-discovers `architecture/overview.md` if present, so installing both plugins gives you the full five-stage flow. See [CHANGELOG.md](CHANGELOG.md) for migration steps.
+> **v3.0.0 — architect step extracted from this plugin.** The plan command still auto-discovers `architecture/overview.md` if present, so any compatible producer (architect plugin no longer publicly distributed; the architecture/overview.md slot remains available for any compatible producer) plugs into the same slot. See [CHANGELOG.md](CHANGELOG.md) for migration history.
 
 ## Commands
 
@@ -56,7 +56,7 @@ Flags combine: `--project <dir> --local`, `--external --quick`.
 
 **Breaking change (v2.0):** one of `--brief` or `--project` is required. There is no interview inside `/ultraplan-local`. The `--spec` flag has been removed — use `/ultrabrief-local` to produce a brief instead.
 
-If `{project_dir}/architecture/overview.md` exists (typically produced by the separate `ultra-cc-architect` plugin), the plan command auto-discovers it and treats `cc_features_proposed` as priors. Missing file is fine — discovery is additive, not required.
+If `{project_dir}/architecture/overview.md` exists (typically produced by an opt-in upstream architect plugin, not bundled), the plan command auto-discovers it and treats `cc_features_proposed` as priors. Missing file is fine — discovery is additive, not required.
 
 ### /ultraexecute-local modes
 
@@ -173,7 +173,7 @@ Path C migration would require: (1) re-architecting tool-list to be identical ac
 
 **Research:** Foreground workflow (v2.4.0): Parse mode → Interview → Parallel research swarm (5 local + 4 external + 1 bridge, spawned from main context) → Follow-ups → Triangulation → Synthesis + brief → Stats. With `--project`, writes to `{dir}/research/NN-slug.md`.
 
-**Plan:** Foreground workflow (v2.4.0): Parse mode (validate brief input) → Codebase sizing → Brief review (`brief-reviewer`) → Parallel exploration (6-8 agents, spawned from main context) → Deep-dives → Synthesis (with architecture-note cross-reference if present) → Planning → Adversarial review (`plan-critic` + `scope-guardian`) → Present/refine → Handoff. With `--project`, writes to `{dir}/plan.md` and auto-detects `{dir}/architecture/overview.md` (produced by the separate `ultra-cc-architect` plugin if installed).
+**Plan:** Foreground workflow (v2.4.0): Parse mode (validate brief input) → Codebase sizing → Brief review (`brief-reviewer`) → Parallel exploration (6-8 agents, spawned from main context) → Deep-dives → Synthesis (with architecture-note cross-reference if present) → Planning → Adversarial review (`plan-critic` + `scope-guardian`) → Present/refine → Handoff. With `--project`, writes to `{dir}/plan.md` and auto-detects `{dir}/architecture/overview.md` (produced by an opt-in upstream architect plugin if installed; not bundled).
 
 **Decompose:** Parse plan → Analyze step dependencies → Group into sessions → Identify parallel waves → Generate session specs + dependency graph + launch script.
 
@@ -183,15 +183,15 @@ Path C migration would require: (1) re-architecting tool-list to be identical ac
 
 **Security:** 4-layer defense-in-depth: plugin hooks (pre-bash-executor, pre-write-executor), prompt-level denylist (works in headless sessions), pre-execution plan scan (Phase 2.4), scoped `--allowedTools` replacing `--dangerously-skip-permissions`. Hard Rules 14-16 enforce verify command security, repo-boundary writes, and sensitive path protection.
 
-**Pipeline:** `/ultrabrief-local` produces the task brief. `/ultraresearch-local --project <dir>` fills in `{dir}/research/`. `/ultraplan-local --project <dir>` reads brief + research to produce `{dir}/plan.md` (and auto-discovers `{dir}/architecture/overview.md` if the separate `ultra-cc-architect` plugin produced one). `/ultraexecute-local --project <dir>` executes and writes `{dir}/progress.json`. All artifacts live in one project directory.
+**Pipeline:** `/ultrabrief-local` produces the task brief. `/ultraresearch-local --project <dir>` fills in `{dir}/research/`. `/ultraplan-local --project <dir>` reads brief + research to produce `{dir}/plan.md` (and auto-discovers `{dir}/architecture/overview.md` if an opt-in upstream architect plugin produced one). `/ultraexecute-local --project <dir>` executes and writes `{dir}/progress.json`. All artifacts live in one project directory.
 
-**Project-directory contract (v3.0.0):** ultraplan-local owns the directory layout below. The `architecture/` subdirectory is opt-in and produced by the separate `ultra-cc-architect` plugin — install that plugin to participate in the architect step.
+**Project-directory contract (v3.0.0):** ultraplan-local owns the directory layout below. The `architecture/` subdirectory is opt-in and produced by an opt-in upstream architect plugin (not bundled) — the architect plugin is no longer publicly distributed, but the `architecture/overview.md` slot remains available for any compatible producer.
 
 ```
 .claude/projects/{YYYY-MM-DD}-{slug}/
   brief.md           ← ultrabrief-local writes; everyone reads
   research/*.md      ← ultraresearch-local writes; plan + architect read
-  architecture/      ← OPT-IN, owned by ultra-cc-architect plugin
+  architecture/      ← OPT-IN, owned by an opt-in upstream architect plugin (not bundled)
     overview.md
     gaps.md
   plan.md            ← ultraplan-local writes; ultraexecute reads
@@ -206,7 +206,7 @@ All artifacts in one project directory (default):
 - Project root: `.claude/projects/{YYYY-MM-DD}-{slug}/`
   - `brief.md` (task brief from `/ultrabrief-local`)
   - `research/{NN}-{slug}.md` (research briefs from `/ultraresearch-local --project`)
-  - `architecture/overview.md` + `architecture/gaps.md` (opt-in, produced by the separate `ultra-cc-architect` plugin)
+  - `architecture/overview.md` + `architecture/gaps.md` (opt-in, produced by an opt-in upstream architect plugin, not bundled)
   - `plan.md` (from `/ultraplan-local --project`)
   - `sessions/session-*.md` (from `--decompose`)
   - `progress.json` (from `/ultraexecute-local --project`)
@@ -231,7 +231,7 @@ Stats:
 
 - **Task brief** — produced by `/ultrabrief-local`. Declares intent, goal, and research plan. Drives planning.
 - **Research brief** — produced by `/ultraresearch-local`. Answers a specific research question. Feeds planning.
-- **Architecture note** — opt-in, produced by `/ultra-cc-architect-local` from the separate `ultra-cc-architect` plugin. Proposes which Claude Code features fit the task with brief-anchored rationale + explicit gaps. When present, enriches planning.
+- **Architecture note** — opt-in, produced by an opt-in upstream architect plugin (not bundled; the architect plugin is no longer publicly distributed, but the `architecture/overview.md` filesystem slot remains available for any compatible producer). Proposes which Claude Code features fit the task with brief-anchored rationale + explicit gaps. When present, enriches planning.
 - **Review** — produced by `/ultrareview-local`. Independent post-hoc review of delivered code against the task brief. **Handover 6 (review → plan)** routes BLOCKER + MAJOR findings into `/ultraplan-local --brief review.md` for a remediation plan. The plan's optional `source_findings:` frontmatter list is the audit trail back to the consumed findings. MINOR + SUGGESTION are skipped for v1.0 plan-input.
 - **Session state** — `.session-state.local.json` per project. **Handover 7** — produced by any session-end mechanism (`/ultraexecute-local` Phase 8/2.55/4, `/ultraplan-end-session-local` helper, future graceful-handoff v2.2). Consumed by `/ultracontinue-local` to resume the next session in a fresh chat. Schema v1 is forward-compat (unknown top-level keys ignored). Never committed (gitignored via `*.local.json`).