Validates and persists signal files to the yahoo-mlb signals directory. Every MLB skill calls this skill before writing a signal. Enforces the signal-framework.md schema -- required YAML frontmatter fields (type, date, emitted_by, confidence, source_urls), range-checks numeric signals (0-100 unipolar, -100 to +100 bipolar), verifies variant_synthesis metadata, and enforces file naming. On validation failure, does not persist and routes a failure entry to mlb-decision-logger. Use when an agent or skill needs to emit a signal, validate a signal file, write to signals/YYYY-MM-DD-<type>.md, or check signal frontmatter. Triggers: "emit signal", "validate signal", "write signal file", "signal frontmatter".
Installation
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Validates and persists signal files to the yahoo-mlb signals directory. Every MLB skill calls this skill before writing a signal. Enforces the signal-framework.md schema -- required YAML frontmatter fields (type, date, emitted_by, confidence, source_urls), range-checks numeric signals (0-100 unipolar, -100 to +100 bipolar), verifies variant_synthesis metadata, and enforces file naming. On validation failure, does not persist and routes a failure entry to mlb-decision-logger. Use when an agent or skill needs to emit a signal, validate a signal file, write to signals/YYYY-MM-DD-<type>.md, or check signal frontmatter. Triggers: "emit signal", "validate signal", "write signal file", "signal frontmatter".
Action: Write to yahoo-mlb/signals/2026-04-17-player-caminero.md and return the absolute path.
Failure scenario: If confidence: 1.4 had been passed, validation fails. The skill does NOT write the file. It calls mlb-decision-logger with a failure entry: kind: signal_validation_failure, signal_type: player, reason: confidence out of range (1.4 not in [0.0, 1.0]), emitter: mlb-player-analyzer, and returns an error to the calling agent.
The caller hands in three things: (1) YAML frontmatter key-value pairs, (2) signal body (markdown tables), (3) intent (e.g., "this is a final synthesized signal" vs. "this is an intermediate variant dump"). See resources/template.md for the canonical input shape.
Frontmatter fields collected
Body (markdown tables) supplied
Intent known: final vs. variant-intermediate
Step 2: Validate YAML frontmatter
Confirm all required keys are present and well-typed. See resources/methodology.md for the full list.
type present and in the allowed enum (lineup, waivers, streaming, trade, category-plan, playoff-push, player, matchup, regression, two-start, closer, faab, cat-state)
date present and formatted YYYY-MM-DD
emitted_by present and references a known skill or agent
confidence present as a float in [0.0, 1.0]
source_urls present as a non-empty list of URLs
Step 3: Range-check numeric signals
Every numeric signal in the body must fall inside its declared range. See resources/methodology.md for the per-signal range table (it mirrors signal-framework.md).
Bipolar signals (regression_index, positional_flex_delta) in [-100, +100]
Integer signals (playoff_games) >= 0
Dollar signals (acquisition_value, faab_max_bid, faab_rec_bid) >= 0
Enum signals (cat_position, verdict) inside their declared allowed sets
Step 4: Validate variant synthesis metadata
If this is a synthesized final signal, it must declare which variants produced it.
If variant_synthesis: true, variants_fired is a list with >= 1 entry
If variant_synthesis: true, synthesis_confidence is present and in [0.0, 1.0]
If variant_synthesis: false, the file is an intermediate variant dump; filename must include the variant suffix (see Step 5)
red_team_findings (if present) is a list of objects with severity, likelihood, score, note fields
Step 5: Determine and validate file path
The canonical path is yahoo-mlb/signals/YYYY-MM-DD-<type>.md. For an intermediate variant dump, use YYYY-MM-DD-<type>-<variant>.md. For per-player or per-game files, an optional identifier suffix is allowed: YYYY-MM-DD-<type>-<identifier>.md.
Compute path from date and type in frontmatter
Check that a signal of this type+date does not already exist unless the caller explicitly passed overwrite: true
Ensure the parent directory exists (create if missing)
Reject paths that escape the signals/ directory
Step 6: Write file OR log validation failure
If all checks pass: write the file, return the absolute path. If any check fails: do NOT write, call mlb-decision-logger with a structured failure entry, return an error object to the caller. See resources/methodology.md for the failure log schema.
On pass: write file, return absolute path
On fail: build failure object (reason, field, expected, actual), send to mlb-decision-logger, return error
Required numeric signals in body: daily_quality, plus the three components (form_score, matchup_score, opportunity_score)
Always a final synthesized signal when emitted by mlb-player-analyzer -- so variant_synthesis: true and variants_fired: [advocate, critic]
Source URLs must include Baseball Savant, FanGraphs, and MLB.com (confirmed lineup)
Pattern 2: Daily lineup roll-up (type: lineup)
Filename: YYYY-MM-DD-lineup.md
Body references, by name, the per-player signal files it consumed (provenance chain)
synthesis_confidence reflects agreement between the advocate (bat-everyone) and critic (sit-risky) variants
Red-team findings typically flag weather, role uncertainty, or fragile platoon calls
Pattern 3: Intermediate variant dump (variant suffix in filename)
Filename: YYYY-MM-DD-<type>-advocate.md or YYYY-MM-DD-<type>-critic.md
variant_synthesis: false (this IS a variant, not a synthesis)
emitted_by names the agent and variant (e.g., mlb-lineup-optimizer/advocate)
The synthesizing agent reads these two intermediate files, produces the final synthesized signal, then emits with variant_synthesis: true
Pattern 4: Low-confidence graceful degrade
When a web search fails, the upstream skill should still emit a signal but with confidence <= 0.3 and a red_team_findings entry flagging the missing data source
This skill does NOT reject low-confidence signals -- low confidence is legitimate. It only rejects out-of-range or missing fields.
Flag in body: "Could not verify opposing pitcher; using prior-start proxy."
Guardrails
Never silently drop a signal. If validation fails, the failure must be logged via mlb-decision-logger so the calibration review can see what was rejected and why. A signal that never gets written AND never gets logged is invisible to the team.
Do not re-derive signal values. This skill is a validator and file-writer only. It never computes daily_quality or any other signal itself. If an upstream skill passes in a half-computed signal, reject it rather than filling in the blanks.
Reject unknown type values. The enum in signal-framework.md is the authoritative list. If a caller passes type: vibe-check, reject and log. Adding a new signal type requires updating signal-framework.md first, then this skill's validator.
Range checks are hard limits. A form_score of 105 is not "close enough" -- it indicates a bug upstream (probably forgot to normalize). Reject and log. Do NOT clamp-and-accept.
confidence is required, not optional. Even a perfectly-computed signal with three source URLs must carry a confidence float. A missing confidence is a validator failure, not a warning.
source_urls must be a non-empty list. Per CLAUDE.md rule 1 ("Web-search everything"), every factual signal is backed by a live source. An empty source_urls list means the signal was not grounded -- reject and log.
Variant synthesis claims must be provable. If variant_synthesis: true but variants_fired is empty or missing, that is a lie about the team's process. Reject and log.
Do not overwrite without explicit consent. If a signal already exists at the target path, refuse to overwrite unless the caller passes overwrite: true. This prevents losing an earlier morning's signal when a mid-day re-run happens.
Quick Reference
Required frontmatter fields (always):
type (enum)
date (YYYY-MM-DD)
emitted_by (string)
confidence (float 0.0-1.0)
source_urls (non-empty list)
Required when variant_synthesis: true:
variants_fired (list, >= 1)
synthesis_confidence (float 0.0-1.0)
File path conventions:
Final synthesized: signals/YYYY-MM-DD-<type>.md
With identifier: signals/YYYY-MM-DD-<type>-<id>.md
