Reduce Copilot propagation API pressure

[woksin]

Summary

• limit Copilot propagation matrix concurrency with max-parallel: 3
• fetch source Copilot files once into a workflow artifact and reuse it per target repo
• add a shared gh api retry helper and route propagation API calls through it
• update propagation docs to describe the fetch-once artifact flow

Verification

• bash -n .github/scripts/github-api-retry.sh
• bash -n .github/scripts/prepare-copilot-source-artifact.sh
• bash -n .github/scripts/propagate-copilot-instructions.sh
• bash -n .github/scripts/copilot-sync-ignore-filter.sh
• git diff --check
• ruby -e "require 'yaml'; YAML.load_file('.github/workflows/propagate-copilot-instructions.yml')"
• empty prepared-artifact smoke test exits before target API calls

Note: actionlint is not installed in this workspace, so I could not run it locally.

[woksin]

Additional validation after PR creation:

• Mocked retry helper test confirms a POST using --input - preserves its payload across a rate-limit retry.
• Mocked propagation artifact-mode test confirms an already-up-to-date target exits before any write API calls.
• Live read-only source artifact preparation against Cratis/AI succeeded and produced: files=251, blobs=218.

The live check only read from GitHub and wrote the prepared artifact to a temporary local directory.

[woksin]

Follow-up after inspecting local /Volumes/sourcecode/repos/cratis/AI:

Found that the first PR version handled the canonical .ai/ corpus and most .claude/ files, but it was not complete for the full AI adapter layout. It missed:

• AGENTS.md and .agents/skills for Codex
• directory adapter symlinks .github/skills and .github/prompts
• materializing file adapters such as .github/copilot-instructions.md, .github/instructions/*, .claude/rules/*, and AGENTS.md from their canonical .ai/ targets

Pushed an update that:

• expands the selected source set to include AGENTS.md, .agents/, and directory adapter symlink entries
• materializes file adapters to real content while preserving directory symlinks to the synchronized .ai/ tree
• excludes .claude/settings.local.json
• reuses the same prepared source artifact for propagation, single-repo sync, and bootstrap seeding
• updates the bootstrapped wrapper paths and README docs

Additional validation:

• live read-only artifact preparation against Cratis/AI now finds 255 files and 164 unique blobs
• verified .agents/skills, .github/skills, and .github/prompts remain mode 120000 symlinks
• verified .github/copilot-instructions.md and AGENTS.md are materialized as mode 100644 content from .ai/rules/general.md
• reran shell syntax checks, YAML parse, diff check, retry helper smoke test, artifact-mode no-write propagation smoke test, and bootstrap wrapper decode check