muse reflog — use long IDs in human text output

Problem

_fmt_entry in muse/cli/commands/reflog.py renders commit IDs using short_id (12 hex chars) in the human text output:

def _fmt_entry(idx: int, entry: ReflogEntry, short: int = 12) -> str:
    new_short = sanitize_display(short_id(entry.new_id))
    old_short = (
        "initial"
        if entry.old_id == NULL_COMMIT_ID
        else sanitize_display(short_id(entry.old_id))
    )

This produces output like:

@{0} sha256:3f9a1c2d4e7b  (sha256:9b2e4a1f8c3d)  2026-06-28 14:22:11 UTC  claude-code  fix: off-by-one in total

Every other Muse command that surfaces a commit ID in human text uses long_id — the canonical sha256:<64-hex> form. The reflog is inconsistent and the IDs it displays cannot be passed directly to other commands without risk of prefix collision.

The docstring even contradicts itself: it claims short IDs are used "for consistency with all other Muse commands" when the opposite is true.

Additionally, the short: int = 12 parameter in _fmt_entry is declared but never referenced in the function body — dead parameter, should be removed.

The JSON output layer already uses long_id correctly via _ReflogEntryJson. Only the human text path needs fixing.

Fix

In muse/cli/commands/reflog.py:

1. Replace both short_id(...) calls in _fmt_entry with long_id(...).
2. Remove the unused short: int = 12 parameter.
3. Update the docstring to reflect that full IDs are rendered.
4. Update the format spec comment string at the top of run() docstring (<new_sha12> → <new_sha256>).

Correct output after the fix:

@{0} sha256:3f9a1c2d4e7b9c2a4f1d8e3b6c9f2d1a7e4b8c1f5a9d2e6b3c7f0a4d1e8b2c5f  (sha256:9b2e4a1f8c3d7b4e2c1a5f9d3e7b2c8f1a4e7b3c9f2a6d1e4b8c3f7a0d2e5b98)  2026-06-28 14:22:11 UTC  claude-code  fix: off-by-one in total

Deliverables

• [ ] LI_01 — _fmt_entry uses long_id for new_id; output is sha256:<64-hex>
• [ ] LI_02 — _fmt_entry uses long_id for old_id; "initial" sentinel unchanged
• [ ] LI_03 — Unused short: int = 12 parameter removed from _fmt_entry signature
• [ ] LI_04 — _fmt_entry docstring updated; no stale reference to short IDs or the false "consistency" claim
• [ ] LI_05 — run() docstring format spec updated to reflect full IDs
• [ ] LI_06 — Test: muse reflog human text output contains the full 64-hex commit ID of the most recent entry, not a 12-char prefix

Test file: tests/test_cmd_reflog_long_ids.py

Out of scope

• JSON output — already correct (long_id used in _ReflogEntryJson).
• Any other command's ID rendering.