fix(plugin-dev): read full multi-line description in validate-agent.sh

[AliAltivate]

What

plugins/plugin-dev/skills/agent-development/scripts/validate-agent.sh extracts the agent's description frontmatter with:

DESCRIPTION=$(echo "$FRONTMATTER" | grep '^description:' | sed 's/description: *//')

grep is line-oriented, so this keeps only the first physical line of a multi-line YAML description and drops the continuation lines — which is exactly where the <example> blocks live. Two checks then misfire:

• desc_length is computed on the truncated first line.
• the <example> check (grep -q '<example>') always fails.

So every agent with a multi-line description gets a bogus ⚠️ description should include <example> blocks for triggering — including the repo's own plugin-dev agents (agent-creator, plugin-validator, skill-reviewer).

Why it's more than cosmetic (Linux)

On Linux with bash ≥ 4.1, under the script's set -euo pipefail, the ((warning_count++)) that the false warning triggers evaluates to 0 on the first increment, returns exit status 1, and aborts the script. Running the shipped validator on the repo's own agent-creator.md in bash:5.2:

before — dies right after the false warning, no summary, exit 1:

✅ description: 244 characters
⚠️  description should include <example> blocks for triggering
# (script aborts here; exit code 1)

after — runs to completion, exit 0:

✅ All checks passed!

(On macOS bash 3.2 the script doesn't errexit on (( )), so there the same bug surfaces as just the false warning.)

The fix

Extract the full description block — from the description: line up to the next known frontmatter key — so the length and <example> checks run on the complete value:

DESCRIPTION=$(echo "$FRONTMATTER" | awk '
  /^description:/ { found = 1; sub(/^description: */, ""); print; next }
  found && /^(name|model|color|tools):/ { found = 0 }
  found { print }
')

It stops only at name/model/color/tools, not at generic word: lines, because <example> blocks contain column-0 Context: / user: / assistant: lines that a naive next-key match would trip on.

Verification

Before/after on all 15 plugins/**/agents/*.md:

• 3 false warnings removed (agent-creator, plugin-validator, skill-reviewer)
• code-simplifier — reported character count corrected (no warning or exit-code change)
• 11 files produce byte-identical output; no exit-code changes anywhere
• bash -n clean; the awk program works on BSD awk (macOS) and busybox awk (Alpine)

Out of scope (noted, not fixed here)

The same script has a separate, pre-existing fragility: under set -euo pipefail, grep '^field:' for a missing field and ((count++)) from 0 can each abort the script independently of this bug. Fixing that touches ~12 sites and is a larger change, so I've kept this PR focused. Happy to follow up if that would be useful.

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