Skillscript

The worst authorability failure mode: parser silently swallows a real
directive, author/agent gets zero signal that their logic was discarded.

Perry ran qwen authorability rungs against v0.19.6 and surfaced a real
case. Qwen wrote:

# Skill: greet
# Vars: WHO=world

Hello ${WHO}.

default: stamp
    shell(command="date +'%Y-%m-%d'") -> TODAY

(Ops written directly under default: stamp instead of declaring a
stamp: target first, then default: stamp separately.)

Pre-v0.19.7: compiled cleanly. Zero errors, zero warnings, zero
advisories. Template-only output: "Hello world." — the entire shell
op silently vanished. entryTarget got set to "stamp" (a target that
doesn't exist). Both forms of silent-drop are now loud errors.

The fix — two new parser errors

1. Orphan indented op — an indented op line with no enclosing
   target body raises a tier-1 parse error. Message guides the author
   to declare the target first.
2. Entry target referencing missing target — default: <name>
   where <name> isn't in parsed.targets raises a tier-1 parse error
   with the declared-targets list to help the author self-correct.

Both fire at parse time, so lint preflight + compile both surface them
loud.

What changed

• src/parser.ts — orphan-indented-op guard at the silent-skip site
  (was if (!currentTarget) continue — now pushes a parseError);
  entry-target-existence check after target collection.
• tests/v0.19.4-output-template.test.ts — 5 regression tests pinning
  parser + compile rejection of the malformed shape Perry's qwen
  produced, plus positive tests confirming well-formed skills still
  parse cleanly.

Bug-class lesson

Silent-drop is asymptotic worst-case authorability — the author has no
signal to self-correct, can't get unstuck, just gives up. For the
"agents author skills" thesis where the agent is a small model that
sometimes gets structure wrong, every silent-drop is a give-up
trigger. Worth a permanent discipline rule: a parser path that drops
content unconditionally is a bug. if (X) continue with no error
push is the structural smell.

This is the second discipline lesson banked this v0.19.x series
alongside 69e0f91d (audit all consumers when adding a typed field)
and the v0.19.5 lesson (test the simplest-case shape the design
promises). Three lessons across four hotfix rings.