fix: structured standalone detail for missing map keys (#107)

[felipeofdev-ai]

Summary

• Restructure matcher-combinators.standalone/match :mismatch/detail when map mismatches include missing keys.
• Surface :missing-keys, :missing (expected values), and :unexpected-keys instead of embedding Missing records that read like partial mismatches.
• Add regression tests and README standalone docs.

Why

When an expected map key is absent, the standalone API returned entries like :a #Missing{:expected 1} inside the detail map. That reads like a value mismatch missing an :actual field rather than an absent key — exactly the ambiguity @dchelimsky described in #107 and the TODO in standalone_test.clj.

Example before:

(standalone/match (m/equals {:a 1}) {:b 2})
;; :mismatch/detail {:b #Unexpected{:actual 2}, :a #Missing{:expected 1}}

After:

(standalone/match (m/equals {:a 1}) {:b 2})
;; :mismatch/detail {:value {:b 2}
;;                   :missing-keys [:a]
;;                   :missing {:a 1}
;;                   :unexpected-keys [:b]}

Core match results and pretty-print output are unchanged; only the standalone :mismatch/detail shape changes when missing keys are present. Value mismatches on present keys keep the prior annotated-map shape.

Fixes #107

Test plan

• clojure -M:dev:clj-test:test-runner (78 tests, 0 failures)
• clojure -M:dev:clj-test:test-runner -n matcher-combinators.standalone-test
• Full CI (bb test — cljs + midje)

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— Felipe Oliveira Fernandes · Systems & Agentic AI Engineer
https://github.com/felipeofdev-ai · https://felipeofdev-ai.github.io/

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