Fix: preserve independent intent boundaries

[ivory-code]

Summary

• Partition commitless mixed diffs by anchored repository evidence instead of collapsing all residual files into one intent.
• Keep distinct commits that edit one shared source file separate, including exact literal navigation evidence.
• Preserve separate intent-backed QA flows through downstream flow deduplication.

Behavioral Contract

• Unrelated changed files remain separate unless a path, changed symbol, or explicit flow annotation anchors their relationship.
• Common imports, accessibility attributes, UI controls, and broad routing verbs cannot join independent changes.
• Separate intents that edit one route registry retain their own destination evidence and final QA flow.
• Related multi-file behavior and cleanup-tip ranking continue to work as before.

Evidence

Closes #242.

Positive and negative coverage:

• web-independent-diff-intents
• web-independent-route-commits
• release-shaped web changes recover diff-first sharing, access, time, media, and storage QA
• web-preferences-cleanup-tip
• long-pr-independent-intents

Checks

Check only what applies. Mark the rest N/A in Review Notes.

• Focused regression test
• pnpm test
• pnpm bench:ci for inference, routing, trace, or output
• pnpm bench:execution for E2E compiler or execution fixtures
• pnpm scan for scanner, security, or repository policy
• pnpm plugin:check and pnpm plugin:smoke for plugin changes
• Documentation links and commands verified

Public OSS Check

• No private repository, source, path, customer data, credential, or internal smoke output is included.
• Shared inference has unrelated positive and negative coverage, or this is not applicable.
• User-facing commands and claims match actual behavior.

Review Notes

pnpm check and git diff --check also pass. pnpm bench:execution, pnpm scan, and plugin checks are N/A because this change does not modify execution compilation, scanner policy, security policy, or plugin packaging. A static QAMap comparison selected the focused change-intent suite and pnpm bench:ci; it remained correctly marked not-run, and both commands were executed independently.