# ECP-0090: PAT-Derived Broadcast Identity Promotion

Status: Implemented

## Decision

Extend default discovery identity synthesis to probe early MPEG-TS packets for Program Association Table (PAT) data and use that to strengthen broadcast-scoped stream IDs.

Current rule:

- If source/channel metadata already yields a usable broadcast identity, use it.
- If transport probing finds PAT data, fill missing `transport_stream_id` and `program_number`.
- If PAT shows exactly one non-zero program, that program is eligible for broadcast-scoped convergence.
- If PAT is ambiguous (multiple non-zero programs), do not guess; keep `program_number` unset and fall back to source scope when needed.
- If the probe sees ATSC PSIP traffic, label the standard as `atsc`; otherwise use a generic `mpegts` fallback when PAT is the only signal.

## Motivation

ECP-0089 fixed the first duplication bug by preferring channel metadata over source-local IDs. That still left a hole:

- raw TS sources without lineup metadata could not converge,
- channel metadata could be incomplete or inconsistent,
- and weak identity inputs risked accidental convergence on the wrong broadcast.

PAT-derived identity gives us a stronger on-wire fingerprint without waiting for full PSIP/VCT parsing.

## Scope

In scope:

- PAT parsing in `ec-ts`
- bounded transport probing for `tsid` / single-program extraction
- source integration for raw TS inputs and HDHomeRun enrichment
- tests that enforce "single program promotes, ambiguous stream does not"

Out of scope:

- full ATSC VCT/MGT descriptor parsing
- DVB service table parsing
- cryptographic origin authentication for discovery announcements

## Alternatives considered

- Keep trusting channel metadata only. Rejected because it leaves raw TS paths weak and incomplete.
- Always promote from PAT even with multiple programs. Rejected because it guesses the channel and increases junk-collision risk.
- Require manual `--stream-id` for TS inputs. Rejected because it pushes canonicalization burden onto operators.

## Rollout / Reversibility

- Additive and reversible: explicit `--stream-id` still overrides everything.
- Roll back by removing PAT probing and returning to metadata-only promotion.
- Future PSIP/VCT work can refine the broadcast identity without changing the override surface.
