fix: Fix mixed signer/non-signer handling in post-delegation actions

[snawaz]

• fix cleartext_with_insertable construction so an inserted non-signer reused later as a signer gets a signer slot, while inserted signers can still be reused by later non-signer metas. Now the construction ensures that:
  • signer metas must use signer storage; this may cause a pubkey to be added twice: 1) first as a non-signer from the insertable actions, 2) and second as a signer from the new instructions.
  • but non-signer metas may safely reuse signer storage. we do not add pubkey twice in this case even if signer is from the insertable actions, and non-signer from the new instructions.
• relax validation to enforce the correct one-way signer invariant: only signer metas must resolve to signer storage (non-signers can resolve to any storage), and signer-storage pubkeys must be backed by signed AccountInfos.

ref: https://explorer.solana.com/tx/2Kkr1hazsZXJ92qi8xL3cXLbx3f2gYr7c6iHcTvu2fH65pE45uqJ5P7UXpVAAhRGGVemPFvJNoGxBoS9AKksJ7ej

Summary by CodeRabbit

• Bug Fixes
  • Improved signer handling when compacting delegated account metadata.
  • Prevented signer accounts from being incorrectly dropped or assigned incorrect indexes.
  • Enhanced validation to ensure signer accounts resolve to valid signer storage.
  • Added coverage for reusing inserted signer entries as non-signer metadata while preserving signer recognition.

[snawaz]

• fix: Fix mixed signer/non-signer handling in post-delegation actions #187 👈 (View in Graphite)
• main

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• dlp-api/src/compact/mod.rs

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📝 Walkthrough

Walkthrough

Updated cleartext compaction to preserve signer-storage indexing when insertable pubkeys are reused. Delegated-action validation now requires signer metas to resolve to signer storage while allowing non-signer metas to reference signer storage. Added signer security-model documentation and tests covering these cases.

Suggested reviewers: gabrielepicco

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• Create PR with unit tests
• Commit unit tests in branch snawaz/fix-indexing

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
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Inline comments:
In `@dlp-api/src/compact/mod.rs`:
- Around line 307-318: Document the invariant in the index_of_signer closure
before the signers.iter().position(...).unwrap() call, explicitly stating that
every non-skipped signer is inserted into signers before this closure runs. Keep
the existing lookup behavior unchanged while making the unwrap’s safety
assumption clear, matching the explanatory style of the sibling index_of
closure.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

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• dlp-api/src/compact/mod.rs