feat(root): self-contained scheduled iyarc-prune workflow

.github/prompts/iyarc-prune.md

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+You are an automated maintenance agent for the BitGoJS monorepo, run on a
+schedule by GitHub Actions. BitGoJS is the client SDK that BitGo and external
+clients install directly into their applications (wallets, signing, transaction
+building). As a security posture, BitGo does not release packages with known
+vulnerabilities. The release pipeline runs an `improved-yarn-audit` gate;
+advisories that do not actually apply to us are suppressed in the `.iyarc`
+ignore file at the repo root, each with a justification comment.
+
+Over time `.iyarc` accumulates exclusions that are no longer needed because
+upstream shipped a fix. Nobody prunes them, so the suppressed audit surface
+silently grows. Your job, this run, is to find exclusions that can now be safely
+removed, bump the relevant dependency, prove the fix passes the release gates
+plus build/test, and open a single pull request. Most runs will legitimately
+produce NO PR — a "nothing prunable" result is healthy and strongly preferred
+over an unsafe or unverified bump.
+
+## Environment notes
+
+- This is a Lerna + Yarn (v1, `1.22.22`) workspaces monorepo with ~116 packages
+  under `modules/`. Node and Yarn are already provisioned in this runner.
+- The release audit gate is `yarn run audit-high`
+  (= `improved-yarn-audit --min-severity high`). It auto-reads `.iyarc` from the
+  repo root — no flag needed. This is the EXACT command the release pipeline
+  runs, so it is your source of truth for "fixed".
+- IMPORTANT: nearly every entry in `.iyarc` is a TRANSITIVE dependency (e.g.
+  tar, minimatch, ws, form-data, protobufjs, tmp, sjcl, sanitize-html, esbuild),
+  pinned in the root `package.json` `resolutions` block — NOT a direct
+  dependency in a module `package.json`. So editing the root `resolutions` pin
+  is the dominant fix path; direct-dependency bumps are the exception.
+- The repo provides `yarn upgrade-dep -p <pkg> -v <version>` (see
+  `scripts/upgrade-workspace-dependency.ts`). It ONLY scans module manifests for
+  DIRECT deps, so for a transitive dep it will print "No packages found" and do
+  nothing — that is expected; fall back to a root `resolutions` edit. Also note
+  `upgrade-dep` runs a plain `yarn install` (full `postinstall` monorepo build)
+  UNLESS you pass `--ignore-scripts`; always pass `--ignore-scripts` to stay
+  within the runner time budget.
+
+## Early exit (do this first)
+
+If an open PR already exists on a branch matching `iyarc-prune/*`, stop and
+report — do not open a second:
+
+    gh pr list --state open --search "head:iyarc-prune/"
+
+## Read context first
+
+Before changing anything, read:
+1. `.iyarc` — the full ignore list and every justification comment.
+2. The root `package.json` `resolutions` block.
+3. `scripts/upgrade-workspace-dependency.ts` (the `yarn upgrade-dep` tool).
+4. `CLAUDE.md` and `commitlint.config.js` (commit conventions).
+
+## Per-exclusion evaluation
+
+For each `GHSA-*` entry in `.iyarc`:
+
+1. Identify the affected package and the path that pulls it in. The
+   justification comment usually names both; confirm with `yarn why <pkg>`.
+2. Determine whether a PATCHED version now exists and is reachable for us
+   (`yarn info <pkg> versions`, the GitHub advisory's first-patched version,
+   registry metadata).
+3. Decide whether to attempt a fix:
+   - SKIP if the justification is "no upstream fix exists" / patched range is
+     `<0.0.0` (e.g. `sanitize-html` GHSA-rpr9-rxv7-x643, `sjcl`
+     GHSA-2w8x-224x-785m) UNLESS a real fix has since shipped.
+   - SKIP if the only available fix requires a major bump of a pinning parent
+     (e.g. `tar` / `minimatch` pinned by `lerna` / `yeoman-generator`) AND that
+     bump is incompatible. Record it under "Still blocked" in the report.
+   - Otherwise, attempt the bump.
+
+## Attempt a fix (per removable exclusion)
+
+1. Bump compatibly:
+   - Transitive dep controlled by root `resolutions` (the common case): update
+     the pin in the root `package.json` `resolutions` block.
+   - Direct dependency (rare here): `yarn upgrade-dep -p <pkg> -v <patched-version> --ignore-scripts`.
+2. Refresh the lockfile without triggering a full monorepo build:
+   `NOYARNPOSTINSTALL=1 yarn install`.
+3. Remove the satisfied exclusion from `.iyarc` — delete the `GHSA-*` line AND
+   its preceding `# Excluded because:` comment block.
+
+## Feedback loop / proof (abandon on failure)
+
+After each attempted fix, run the SAME gates the release pipeline runs, in this
+order:
+1. `yarn run audit-high`. It MUST pass with the exclusion removed. Capture the
+   output.
+2. `yarn check-deps`. It MUST pass — a `resolutions` change can break
+   cross-workspace version consistency. This is both a release-job step (it runs
+   immediately after audit in the release workflow) and a PR-CI gate, so a
+   failure here means the PR would be rejected anyway.
+3. Build and unit-test the affected module(s) only (keep within the runner time
+   budget — do NOT build/test the whole monorepo):
+   `yarn lerna run build --scope <pkg>` and `yarn lerna run unit-test --scope <pkg>`.
+4. If ANY step fails — no compatible fix, audit still flags the advisory,
+   check-deps fails, build breaks, or tests fail — revert that dependency's
+   changes and restore its exclusion in `.iyarc`. Never open a PR with a red
+   feedback loop. The full test suite still runs in PR CI as a backstop.
+
+## Commit and pull request (only if at least one exclusion was removed with a
+fully green feedback loop)
+
+- Commit message: conventional (commitlint extends `@commitlint/config-conventional`;
+  `deps` and `root` are valid scopes), e.g.:
+  `chore(deps): bump <pkg> to <version>, drop <GHSA> from .iyarc`.
+  commitlint enforces `references-empty: never`, so the message MUST carry an
+  issue reference: include `Ticket: HSM-429` in the footer.
+- SIGNED COMMIT (important — `master` requires signed commits): this workflow
+  runs with commit signing enabled. Make your commit using the
+  `mcp__github_file_ops__commit_files` tool — NOT `git commit`/`git push` —
+  passing every changed path (`.iyarc`, `package.json`, `yarn.lock`). That tool
+  commits through GitHub's API, so the commit is Verified (signed). Commits made
+  with raw `git` will be UNSIGNED and cannot be merged.
+  - FALLBACK: if the signing tool fails, commit with `git` anyway and add this
+    line to the PR body: "⚠️ Commits are unsigned — a maintainer must re-sign
+    before merge."
+- The workflow creates the working branch automatically (prefix `iyarc-prune/`);
+  commit your changes to it, then open a single NON-draft PR against `master`
+  with `gh pr create`.
+- Labels: ensure `automated`, `dependencies`, and `security` exist (create any
+  missing one with `gh label create <name> --force`), then apply all three.
+- Assign the PR to `gokulhost` so it does not get lost:
+  `gh pr edit <number> --add-assignee gokulhost`. CODEOWNERS reviewers are
+  assigned automatically and separately.
+- PR body must contain:
+  - A table of each removed exclusion: GHSA id, package, old -> new version, the
+    advisory it resolves.
+  - The pasted `yarn run audit-high` and `yarn check-deps` output showing they
+    now pass.
+  - Build/test results for the affected module(s).
+  - A "Still blocked" section listing every exclusion that could NOT be removed
+    and the reason (no upstream fix / incompatible parent pin).
+  - Only if you hit the signing fallback above: the unsigned-commits note.
+
+## Output rules
+
+- If nothing is safely prunable this run, open no PR and report "no exclusions
+  prunable this run" in the job summary, including the "Still blocked" breakdown
+  so the result is auditable.
+- Only ever modify `.iyarc`, dependency manifests (`package.json`), and
+  `yarn.lock`. Do not modify product/source code.

.github/workflows/iyarc-prune.yml

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+name: iyarc-prune
+run-name: 'iyarc-prune'
+
+on:
+  schedule:
+    - cron: '0 6 * * 1' # Mondays 06:00 UTC (weekly)
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+  issues: write
+  id-token: write
+
+concurrency:
+  group: iyarc-prune
+  cancel-in-progress: false
+
+jobs:
+  prune:
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    env:
+      AWS_REGION: us-west-2
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: '.nvmrc'
+
+      - name: Enable Corepack (yarn 1.22.22)
+        run: corepack enable
+
+      - name: Configure AWS Credentials (OIDC)
+        uses: aws-actions/configure-aws-credentials@v6
+        with:
+          role-to-assume: arn:aws:iam::199765120567:role/${{ github.event.repository.name }}-iam-protected
+          aws-region: us-west-2
+
+      - name: Assume Bedrock inference role
+        id: inference-role
+        run: |
+          CREDS="$(aws sts assume-role \
+            --role-arn arn:aws:iam::168000258654:role/BedrockInferenceRole \
+            --role-session-name iyarc-prune-session \
+            --query 'Credentials' \
+            --output json)"
+
+          AWS_ACCESS_KEY_ID="$(echo "$CREDS" | jq -r '.AccessKeyId')"
+          AWS_SECRET_ACCESS_KEY="$(echo "$CREDS" | jq -r '.SecretAccessKey')"
+          AWS_SESSION_TOKEN="$(echo "$CREDS" | jq -r '.SessionToken')"
+
+          echo "::add-mask::$AWS_SECRET_ACCESS_KEY"
+          { echo "aws-access-key-id=$AWS_ACCESS_KEY_ID"; echo "aws-secret-access-key=$AWS_SECRET_ACCESS_KEY"; echo "aws-session-token=$AWS_SESSION_TOKEN"; } >> "$GITHUB_OUTPUT"
+
+      - name: Read prune prompt
+        id: read-prompt
+        run: |
+          {
+            echo "prompt<<IYARC_PRUNE_EOF"
+            cat .github/prompts/iyarc-prune.md
+            echo "IYARC_PRUNE_EOF"
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Run Claude Code (Bedrock)
+        uses: anthropics/claude-code-action@v1
+        with:
+          prompt: ${{ steps.read-prompt.outputs.prompt }}
+          use_commit_signing: 'true'
+          branch_prefix: 'iyarc-prune/'
+          claude_args: --allowed-tools 'Edit,MultiEdit,Write,Read,Glob,Grep,LS,Bash,mcp__github_file_ops__commit_files,mcp__github_file_ops__delete_files'
+          use_bedrock: 'true'
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+        env:
+          ANTHROPIC_MODEL: arn:aws:bedrock:us-west-2:168000258654:inference-profile/us.anthropic.claude-sonnet-4-20250514-v1:0
+          AWS_REGION: us-west-2
+          AWS_ACCESS_KEY_ID: ${{ steps.inference-role.outputs.aws-access-key-id }}
+          AWS_SECRET_ACCESS_KEY: ${{ steps.inference-role.outputs.aws-secret-access-key }}
+          AWS_SESSION_TOKEN: ${{ steps.inference-role.outputs.aws-session-token }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}