fix(portal): unbounded sources anchor the backfill floor at genesis (C10, ports #8)

[dzhelezov]

Ports the backfill-floor fix (the one historical-path finding) from open PR #8 by @mo4islona onto current main. The other four findings in #8 are Portal stream-realtime hardening and stay with that PR.

The bug

An undefined fromBlock means "from genesis" — ponder's runtime reads filter.fromBlock ?? 0 throughout. But compileFetchSpec's backfillStart took Math.min over only the defined fromBlocks:

const froms = fs.map((f) => f.fromBlock).filter((b) => b != null);
const backfillStart = froms.length ? Math.min(...froms) : 0;

So a config mixing one bounded source (fromBlock: 15_000_000) with one unbounded source (no fromBlock) computed backfillStart = 15M. chunkRange (portal-chunks.ts) then clamps every chunk's low bound to >= 15M, so the unbounded source's [0, 15M) intervals are assembled empty and marked synced -- a permanent silent gap on the production historical path, losing the whole pre-15M history of the unbounded source.

The fix

If any filter omits fromBlock, the floor is 0 -- symmetric with the existing backfillEnd rule directly below it (any undefined toBlock => unbounded):

const froms = fs.map((f) => f.fromBlock);
const backfillStart =
  froms.length && froms.every((b) => b != null)
    ? Math.min(...(froms as number[]))
    : 0;

Re-expressed for the post-refactor compileFetchSpec (PR #8 predates the invariant-first re-architecture, where this lived inline in createPortalHistoricalSync). Added to the invariant catalog as INV-16 (Backfill-floor genesis semantics) in portal/INVARIANTS.md.

Tests (mutation-verified -- both fail on the pre-fix source)

• portal-filters.test.ts -- INV-16/C10: backfillStart is 0 for an undefined fromBlock, min when all defined, 0 for a mixed config.
• portal.test.ts -- C10 regression (ported from fix(portal): close silent-gap paths in backfill floor + stream realtime #8's C10 test): two log sources, one fromBlock: 15M, one undefined; the undefined source's block-100 log is fetched and inserted.

Mutation proof -- reverting only the source fix to the pre-fix Math.min-over-defined-only and re-running the two files in the built tree:

x portal-filters.test.ts > INV-16/C10 ...
  -> expected 15000000 to be +0
x portal.test.ts > regression: an undefined fromBlock is genesis ... (C10) ...
  -> expected [] to have a length of 1 but got +0   <- the silent gap
 Test Files  2 failed (2)
      Tests  2 failed | 27 passed (29)

Restoring the fix returns both files to green (29 passed).

Gate results

Full Portal suite via scripts/sync-upstream.sh <ver> --test (biome check + fresh clone + build + vitest), both compat.tested versions:

Version	Result
0.16.6	15 files, 134 tests passed
0.15.17	15 files, 134 tests passed

• biome check portal/ --diagnostic-level=error: clean (32 files, 0 errors).
• Secret scan (grep -rnE 'prt_int_|prt_euler_|sqd_rpc_[A-Za-z0-9]{10}'): no matches.

Credit: original fix by @mo4islona in #8; this PR ports just the C10 backfill-floor finding, with a focused unit test added on compileFetchSpec.

Generated with Claude Code