fix(load): consume blank before-load hook replacements

[ss-o]

Problem

(z) splits a blank string into one empty word. A before-load hook that
consumed its final request successfully and returned an empty
ZI[annex-before-load:new-@] therefore reached the loader as a blank object
ID, and the dispatcher reported No plugin or snippet ID given (zi.zsh:3086)
with status 2 instead of succeeding with nothing loaded.

Verified directly:

raw=[]    count=1 elems=''
raw=[  ]  count=1 elems=''
raw=[x  ] count=1 elems='x'

Change

Drop the word when the replacement holds no non-whitespace character. The test
is the whitespace-stripped string, not -n, because whitespace-only splits to
the same single blank word and would otherwise slip through.

The same split affects ZI[annex-before-load:new-global-ices] at the sibling
call site: a blank ice-list became a one-element array, failed the even-count
check, and cost a spurious Bad new-ices returned warning plus 7 added to the
return status. Same guard applied there.

Quoted non-empty replacements, following requests, and odd hook failure
statuses are unchanged.

Verification

• Full tests/ suite: 26 files, all pass. zsh -n clean on both changed files.
• scripts/public-contract-impact.zsh against next: no public-contract
  changes detected.
• Three negative runs, each confirming a distinct guard is actually covered:
  • guard removed at new-@ fails the plain-empty case
  • guard removed at new-global-ices fails the blank-ice-list case
  • guard narrowed back to -n fails the whitespace case, which is what makes
    the widening load-bearing rather than cosmetic

Acceptance

• Empty successful replacement returns zero and loads no object.
• Empty failed replacement preserves the hook error (status 3).
• A following request and a quoted non-empty replacement retain their
  arguments and execute normally.
• Native Zsh syntax and the focused dispatcher/load tests pass.
• Recheck meta-plugins first expansion, retry, and repeated-group behavior
  against the corrected dispatcher.

Open item for review

The last box is deliberately unchecked. It is a cross-repository recheck that
belongs to z-shell/z-a-meta-plugins#60, which is blocked by this issue and runs
after it. A synthetic zi-plus-annex harness did not reach the all-members-loaded
state: with ._zi markers present and members listed in zsh_loaded_plugins,
the handler still queued every member, so $loaded_plugins[(I)$p] is not
matching as expected at handler line 200. That is a hint for whoever builds the
real integration fixture, not a defect claim in this change.

This pull request therefore references the issue rather than closing it. Leave
#511 open until that recheck lands alongside z-shell/z-a-meta-plugins#60.

Refs #511

[Copilot]

🟢 Approval recommended

The reviewed changes address the reported issue and include regression coverage.

Pull request overview

Fixes before-load hook handling so blank replacements no longer become invalid object IDs or malformed ice lists.

Changes:

• Handles blank and whitespace-only replacements safely.
• Preserves failure, follow-up, and quoted replacement behavior.
• Adds focused regression coverage.

File summaries

File	Summary
zi.zsh	Guards blank hook replacements and ice lists.
tests/load-object-status.zsh	Adds focused dispatcher regression tests.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite (auto)

Note

Copilot is running an experiment and ran this review at Lite.

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