Empirical failure: add_library('Standard') on a project that already had Standard, * (System) silently created a SECOND direct Standard reference, pulling in unresolved transitive deps (e.g. yellow-warning IoStandard 3.1.3.1).
Root cause: script always called add_library() without checking lm.references first; never called add_placeholder() so the result was a direct (non-* (System)) reference.
Fix: (1) walk lm.references for an existing entry by bare name and no-op with a confirmation message unless force=true; (2) default to add_placeholder() so transitive deps resolve at compile (matches the modern '<Name>, * (System)' convention); (3) keep add_library() reachable via direct=true; (4) on miss, dump dir(lm) so unknown SPs surface the actual API.
Docs: https://content.helpme-codesys.com/en/ScriptingEngine/ScriptLibManObject.html
Mildly breaking for callers: previous behaviour was always direct
add_library(); pass direct=true to restore. The dedup default also flips
'add second copy' to 'no-op' -- pass force=true to restore.
Test updated: tests/integration/e2e.test.ts now passes USE_DIRECT='0' and
FORCE_DUP='0' alongside LIBRARY_NAME, asserts add_placeholder + dedup
strings appear in the rendered script.
### Manual smoke test
1. mcp__codesys__add_library libraryName=Standard against a project that
already has Standard listed: expect SCRIPT_SUCCESS with body 'Library
Already Present: Standard' and NO second entry in the Library Manager.
2. mcp__codesys__add_library libraryName=Util on a project without Util:
expect a new entry rendered as 'Util, * (System)' (placeholder, not
direct).
3. mcp__codesys__add_library libraryName=Standard direct=true: expect a
direct (non-* (System)) reference even on dedup hit if also force=true.
4. mcp__codesys__list_project_libraries should reflect each result.
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