fix(anthropic): bound retained image position keys

[luvs01]

Motivation

• Close a process-persistent memory-growth vulnerability where attacker-controlled, unbounded media-type strings were embedded verbatim in the in-memory position-store keys, allowing retained-key heap exhaustion across requests.

Description

• Replace variable-length media-type keys with fixed-size SHA-256 identities computed over the image bytes and a canonicalized, length-bounded media type so caller-controlled metadata cannot grow keys unbounded.
• Introduce a PositionEntry shape tracking sizeBytes and storedAt, maintain positionBytes accounting, and delete/evict position entries with deletePositionEntry() to keep byte accounting accurate.
• Integrate the position-store accounting into the existing retained-store snapshot and oldest-entry eviction path so the app-owned memory budget can observe and evict position-store bytes alongside the encode cache.
• Add a regression test asserting that megabyte-scale media-type inputs only cost a small, fixed amount of retained bytes and update the transports inventory note to document the fixed-size identity and accounting change.

Testing

• Ran the focused image-normalize tests with node_modules/bun/bin/bun.exe test tests/adapters/anthropic/anthropic-image-normalize.test.ts, which passed (32 tests) when executed with the repo Bun (1.4.0).
• Ran PATH="$PWD/node_modules/bun/bin:$PATH" bun run typecheck, bun run structure:check, and bun run privacy:scan, all of which passed.
• Ran PATH="$PWD/node_modules/bun/bin:$PATH" bun test tests/ci-workflows/file-size-ratchet.test.ts, which passed; the full bun run test execution produced unrelated environment/concurrency failures and was stopped after observing unrelated flakes.

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Codex Task

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-21T00:29:35.380159Z	2554e18	PR opened

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[github-actions]

✅ Deterministic PR hygiene checks passed.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.