fix(compliance): define capture_path_not_resolvable / unresolved_substitution output shapes

[bokelley]

Closes #3796

Summary

Two grading codes (capture_path_not_resolvable, unresolved_substitution) were defined in storyboard-schema.yaml but had no corresponding output shape in runner-output-contract.yaml. Without normative output shapes, runners had no spec to implement against — and in practice silently swallowed context-extraction failures, reporting them as downstream substitution skips rather than as failures on the capturing step. The diagnostic pointed at the wrong place.

Root symptom (from #3796): signal_marketplace storyboard, step search_by_spec returns a shape-valid but empty signals: [] response. The runner doesn't fail search_by_spec; instead activate_signal steps appear as Skipped: unresolved context variables: first_signal_agent_segment_id, first_signal_pricing_option_id, making it look like the activation handler is missing when the signals handler broke the contract.

Changes

runner-output-contract.yaml (v1.1.0 → v1.2.0)

• Adds capture_path_not_resolvable and unresolved_substitution to the validation_result.check enum. Both appear in validations[] so the existing "failed steps MUST include at least one validation result with passed: false" invariant is satisfied without a contract amendment.
• Documents expected/actual/json_pointer semantics for each code.
• Clarifies that null and "" are equally non-resolvable as an absent path for captures — capturing a null value produces fabricated downstream state.
• Adds pre-wire null carve-outs on request, response, and json_pointer for unresolved_substitution (no request was sent; no response exists).
• Adds run_summary note that capture failures contribute to steps_failed, not steps_skipped.

storyboard-schema.yaml

• Strengthens the context_outputs runner-behavior note to cover absent/null/"" and cross-references runner-output-contract.yaml for the output shapes.
• Expands capture_path_not_resolvable and unresolved_substitution grading-code descriptions with the three non-resolvable value cases and output shape pointers.

signal-marketplace/index.yaml

• Adds explicit field_present guard on signals[0] and signals[1] before deeper-path checks in search_by_spec, so empty/short-array responses fail the capturing step rather than cascading as downstream substitution skips.

Non-breaking justification: Additive only — new check enum values that conformant runners currently do not emit; new inline semantics clauses; no existing check value behavior changed. Runners not yet implementing these codes remain conformant for their current output; the contract now gives them a target to implement against.

Pre-PR review:

• code-reviewer: approved — fixed one blocker (pre-wire null carve-outs on request/response/json_pointer for unresolved_substitution); one nit addressed (signals[1] guard added)
• ad-tech-protocol-expert: approved — check-enum placement correct given the passed: false invariant; null/"" semantics correctly close the loophole; v1.2.0 minor bump correctly scoped

Sibling-repo fix needed: The runner bug (silently swallowing capture failures instead of emitting capture_path_not_resolvable) lives in adcp-client. This PR ships the normative spec the runner needs; the adcp-client runner implementation is the load-bearing follow-up that stops the symptom described in #3796.

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See #3121
for context.

Session: https://claude.ai/code/session_01Wxmx2xnsUoMwMPY4e5Figj

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Generated by Claude Code

[bokelley]

Closing in favor of the unified landing in #3813 — spec + runner ship together so the user-visible symptom in #3796 actually gets fixed. The signals[0]/signals[1] field_present workarounds become unnecessary once the runner emits capture_path_not_resolvable against the capturing step.