[Bug] Plugin agent loader silently filters agents below undocumented system prompt length threshold

Bug Description
Plugin agent loader silently drops agents whose system prompt body falls below an undocumented length threshold. Agents ship to the plugin cache and pass YAML validation but never appear in /agents or as dispatchable subagent_type values.

Observed empirically in the rccs plugin (CyanoTex/Roblox-Claude-Code-Skills):

• 23-line, ~1,173-char bodies consistently filtered out
• 69-line, ~7,355-char bodies register
• 107-line, ~10,910-char bodies register

All filtered and non-filtered agents had identical YAML frontmatter (name, description: |, model: inherit), UTF-8 encoding, valid YAML. Only difference was body prose length and content. Filtered bodies tended to read as "invoke the X skill" thin wrappers.

Neither the sub-agents docs (https://code.claude.com/docs/en/sub-agents) nor plugins-reference (https://code.claude.com/docs/en/plugins-reference) mention a minimum-body rule or a content-based heuristic. Please either document the threshold (exact value, whether it's char/line/token-based, whether frontmatter counts) or remove the filter so plugin authors can ship thin wrapper agents when delegation to a skill is the intentional design.

Environment Info

• Platform: win32
• Terminal: null
• Version: 2.1.104
• Feedback ID: 16683388-9d15-4ea2-87fe-af1356e95a3d

Errors

[{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\code-quality-scorer for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-12T13:23:07.859Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\datastore-performance-auditor for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-12T13:23:07.859Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\memory-auditor for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-12T13:23:07.859Z"},{"error":"Error: ENOENT: no such file or directory, unlink 'C:\\Users\\Cyano\\AppData\\Local\\Temp\\claude\\C--src-Roblox-Claude-Code-Skills\\dfe20b21-246e-467d-a051-f219582dc0de\\tasks\\aea08e04e73bf35de.output'\n    at async <anonymous> (B:/~BUN/root/src/entrypoints/cli.js:7823:299)","timestamp":"2026-04-13T01:30:15.264Z"},{"error":"MaxFileReadTokenExceededError: File content (12385 tokens) exceeds maximum allowed tokens (10000). Use offset and limit parameters to read specific portions of the file, or search for specific content instead of reading the whole file.\n    at _O_ (B:/~BUN/root/src/entrypoints/cli.js:4500:12874)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:30:28.899Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\code-quality-scorer for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:44:37.962Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\datastore-performance-auditor for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:44:37.962Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\memory-auditor for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:44:37.962Z"},{"error":"Error: Request was aborted.\n    at uR8 (B:/~BUN/root/src/entrypoints/cli.js:1325:12089)\n    at next (native:1:11)\n    at mm_ (B:/~BUN/root/src/entrypoints/cli.js:7964:9109)\n    at next (native:1:11)\n    at Um_ (B:/~BUN/root/src/entrypoints/cli.js:7969:12068)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:45:20.814Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\code-quality-scorer for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-13T01:58:19.155Z"},{"error":"Error: Plugin component file not found: C:\\Users\\Cyano\\.claude\\plugins\\cache\\rccs-marketplace\\rccs\\efa0a1956df1\\skills\\datastore-performance-auditor for rccs\n    at TD_ (B:/~BUN/root/src/entrypoints/cli.js:4729:13397)\n    at processTicksAndRejec…

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