fix(sync): reuse deep URL branch cache

[christso]

Summary

• derive the fetch branch from /tree/<branch>/... and /blob/<branch>/... GitHub URLs when callers do not pass a branch override
• use that effective branch for both the cache key and git clone
• preserve explicit FetchOptions.branch precedence

Problem

fetchPlugin() parsed the branch embedded in a deep GitHub URL but ignored it unless every caller also copied that branch into FetchOptions. A standalone skill URL could therefore use the unqualified repository cache and perform a second full clone instead of reusing its existing @main cache. For the Hermes Agent repository this left allagents update silent long enough to appear stuck.

Verification

• bun test tests/unit/core/plugin.test.ts — 17 passed
• bun run typecheck
• bun run lint — 92 files checked
• bun run build

E2E

From /home/christso/.openclaw/agent-profiles/profiles/scout:

/home/christso/projects/EntityProcess/allagents-skill-sync-update-hang/dist/index.js update

Observed exit 0 in 1.32 seconds and one har-derived-api-client skill synced for Copilot.

Deep-URL cache-key smoke check with an isolated HOME containing only the existing branch-qualified cache:

HOME=/tmp/allagents-skill-sync-repro/home ALLAGENTS_CLONE_TIMEOUT_MS=1 bun -e "import { fetchPlugin } from './src/core/plugin.ts'; const result = await fetchPlugin('https://github.com/NousResearch/hermes-agent/blob/main/optional-skills/web-development/har-derived-api-client', { offline: true }); console.log(JSON.stringify({ action: result.action, cachePath: result.cachePath }));"

Observed action: skipped with cache path ending in NousResearch-hermes-agent@main; no fallback clone was attempted.

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