fix(ci): permissions model — no top-level perms in ci.yml; callers need write

GitHub Actions permission model for reusable workflows: callers must declare
at least the permission level that any job in the called workflow requests.
Since the phpcs job declares 'permissions: contents: write' (for phpcbf
commit-back), all callers must include 'permissions: contents: write' at
their workflow level.

Changes:
- ci.yml: remove top-level permissions block (was: contents: read); phpcs job
  already has job-level contents: write. Docblock now explains the caller
  requirement clearly.
- ci-self-test.yml: add 'permissions: contents: write' at workflow level.
- README.md: adoption snippet now includes the required permissions block.
- Remove diagnostic bisect/minimal test workflows (used to identify the root
  cause of startup_failure; finding: job-level write in reusable workflow
  requires caller to declare write at workflow level).

Confirmed: ci-bisect-caller with permissions: contents: write = SUCCESS.
Confirmed: actionlint 1.7.4 + yamllint 1.38.0 both clean.

Agent-Session: claude/reusable-ci-20260616

.github/workflows/ci-bisect-caller.yml

@@ -1,15 +0,0 @@
-name: CI Bisect Caller v3
-
-on:
-  push:
-    branches: ['claude/**']
-
-permissions:
-  contents: write  # needed for called reusable workflow's phpcs job
-
-jobs:
-  ci:
-    uses: ./.github/workflows/ci-bisect.yml
-    with:
-      tests: none
-    secrets: inherit

.github/workflows/ci-bisect.yml

@@ -1,27 +0,0 @@
-name: CI Bisect Test v3
-
-on:
-  workflow_call:
-    inputs:
-      tests:
-        type: string
-        required: false
-        default: stubs
-
-# No top-level permissions — only job-level where needed
-
-jobs:
-  phpcs:
-    name: PHPCS
-    runs-on: ubuntu-latest
-    permissions:
-      contents: write
-    steps:
-      - run: echo "phpcs with write"
-  
-  phpunit:
-    name: PHPUnit
-    runs-on: ubuntu-latest
-    if: ${{ inputs.tests != 'none' }}
-    steps:
-      - run: echo "phpunit ${{ inputs.tests }}"

.github/workflows/ci-minimal-test.yml

@@ -1,12 +0,0 @@
-name: Minimal Reusable Test
-
-on:
-  push:
-    branches: ['claude/**']
-
-jobs:
-  test:
-    uses: ./.github/workflows/ci-minimal.yml
-    with:
-      test_input: hello
-    secrets: inherit

.github/workflows/ci-minimal.yml

@@ -1,18 +0,0 @@
-name: Minimal Reusable
-
-on:
-  workflow_call:
-    inputs:
-      test_input:
-        type: string
-        required: false
-        default: world
-
-permissions:
-  contents: read
-
-jobs:
-  hello:
-    runs-on: ubuntu-latest
-    steps:
-      - run: echo "Hello ${{ inputs.test_input }}"

.github/workflows/ci-self-test.yml

@@ -1,8 +1,9 @@
 # Self-test: exercises the reusable ci.yml on this repo itself.
 # Uses tests: none (peptide-e2e is a Playwright/Node repo, no PHP suite).
-# phpcs_autofix: false avoids needing contents: write at the caller level
-# (the phpcs job in ci.yml has its own job-level write permission for phpcbf).
-# Purpose: smoke-check that the reusable workflow skeleton runs without errors.
+# permissions: contents: write is required at the caller level — any caller of
+# ci.yml must declare this so the phpcs job can commit phpcbf fixes back to the
+# PR branch. Even with phpcs_autofix: false here, the permission must be declared
+# for the reusable workflow to pass GH's startup permission-escalation check.
 
 name: CI Self-Test (reusable ci.yml)
 
@@ -12,6 +13,9 @@ on:
   pull_request:
     branches: [main]
 
+permissions:
+  contents: write  # required: called ci.yml phpcs job declares job-level write for phpcbf
+
 jobs:
   ci:
     uses: ./.github/workflows/ci.yml

.github/workflows/ci.yml

@@ -50,9 +50,11 @@
 #         and concatenated verbatim — missing slash produces wrong path).
 #   - Every repo calls `composer test` regardless of the `tests` input; the
 #     input only controls environment provisioning, not the command.
-#   - permissions: contents: read at workflow level; the phpcs job sets
-#     contents: write for phpcbf commit-back only. Calling workflows do NOT
-#     need to declare contents: write — job-level override is sufficient.
+#   - permissions: the phpcs job declares `contents: write` at job level for
+#     phpcbf commit-back. GitHub requires the CALLING WORKFLOW to also declare
+#     `permissions: contents: write` at the caller's workflow level — GH enforces
+#     that callers cannot be escalated beyond their declared scope, even by job-level
+#     overrides in the reusable workflow. All caller repos must include this.
 ##
 
 name: CI — Reusable
@@ -100,9 +102,6 @@ on:
         default: true
         type: boolean
 
-permissions:
-  contents: read  # jobs that need write declare it explicitly (phpcs)
-
 jobs:
 
   # ---------------------------------------------------------------------------