fix: pr reconcile fails with "ordjson: unsupported type *int" on line-anchored review threads #320

Problem

Since #319 (#306, GitHub review threads), sumctl pr reconcile and sweep fail on any PR that has a review thread anchored to a code line:

error: "ordjson: unsupported type *int"

The review-thread records store optional line numbers as *int (go/internal/prcmd/threads.go:154-157: Line, OriginalLine, StartLine, OriginalStartLine). go/internal/ordjson has no case for pointer-to-int, so encoding the observation fails. sum's own PRs had no line comments, so tests and review missed it.

On 2026-10-19, a sweep failed to observe 29 of 33 recorded open PRs (zumba/salt, zumba/security, zumba/compliance). Cleanup stays blocked for the tasks whose merges can no longer be observed. Reproduce with pr reconcile t-1429ab36f90b --number 2233 (zumba/salt#2233).

Fix

Make a review thread with line anchors encode, persist, read back and display correctly. Unanchored threads keep their current behavior. Choose the smallest fix in the existing style: support nil-able integers in ordjson, or represent the optional lines without pointers. An absent line must stay distinguishable from line 0 wherever that matters today.

Acceptance criteria

• pr reconcile succeeds on a PR whose review threads have line, start line and original-line anchors, and the saved observation keeps those values.
• Context, inbox and status views show anchored threads without error.
• Nothing changes for PRs without review threads or with unanchored threads.