SUBS-034: bare-name argv[0] not realpath'd before sibling-helper lookup

Now: DONE

be launched as a BARE name (argv0="be", no /) resolves via PATH in dog/HOME.c (the bare branch of HOMEResolveSibling, ~l.1054-1084) but looks for the sibling helper (sniff) beside the PATH entry (entry_c), never realpath-ing the found executable. When that be is a symlink into the real bin dir, sniff isn't beside the symlink → home_try_sibling fails → the fallback feeds bare sniff → FILESpawn/execvp fails ENOENT (BEDOGEXIT). The rel/abs branch already realpaths argv0 first (SUBS-022 453c55c2); the bare branch is the residual. Method Issues.

Input

Context

Reproduce: ctest --test-dir beagle/build -R '^be-post-relpath$' --output-on-failure (test be-post-relpath.sh, the SUBS-022 repro).
The test posts via sub-recursion three ways — argv0 as REL path, ABS path, and BARE name. REL+ABS pass; the [bare] arm fails: FILESpawn: exec 'sniff' failed: errno=2 → Error: BEDOGEXIT.
Root cause: dog/HOME.c:1080 calls home_try_sibling(out, entry_c, name) on the raw PATH directory entry; the matching exe (be) is not realpath'd, so a symlinked/relinked be loses the real bin dir that holds sniff.
Pre-flagged in SUBS-033 l.50-51 as a "pre-existing ssh/PATH env issue, unrelated to sniff/" — this ticket is that residual.

Goals

The [bare] arm of be-post-relpath passes; the sibling helper is found beside the REAL binary, not the PATH symlink.
Bare-name self-discovery matches the rel/abs realpath behaviour.

Constraints

Minimal dog/HOME.c fix mirroring the rel/abs realpath path; ABC path discipline — PATHu8bReal + PATHu8sDir, path8b, NO pointer arithmetic (CLAUDE.md §1/§10).
Repro-first (CLAUDE.md §17): the [bare] arm is already a failing repro; keep rel/abs + full ctest green after the fix.

WIP

Design decisions

In the bare branch, after home_is_exe($path(exe)) (HOME.c:1079) realpath exe (PATHu8bReal) → dirname (PATHu8sDir) → home_try_sibling on the REAL dir; fall back to entry_c if realpath fails. Mirror l.1043-1045.
Don't break (l.1081) before the realpath'd dir is tried — let the real dir get its home_try_sibling chance, then break.

TODOs

Confirm [bare] arm fails today (done — exec 'sniff' ENOENT).
Realpath the PATH-resolved exe in the bare branch (HOME.c ~l.1074-1081).
ctest -R '^be-post-relpath$' green incl. [bare]; full suite no regress.

Blockers and bummers

(none known — file-disjoint from the JS path tickets)

Outcome

6df16caa (dog/HOME.c: realpath the PATH-resolved exe in the bare-name branch before the sibling lookup) + 5efa0966 (the deterministic be-sniff-bare-name repro + registration) — landed. be-post-relpath + the new test green; ctest no new regressions.