Where does “briefcase” come from?

I notice some issues with the chain provided that make it impossible to write an accurate sentence: 1. The chain shows "Old French brief" but briefcase is a compound of "brief" + "case," and only "brief" is traced back. The "case" component is missing from the etymological chain. 2. The chain jumps from "Old French brief" to "Latin brevis" to "Latin capio" without explanation—these don't form a coherent derivation path. 3. "Latin capio" (to take/seize) doesn't derive from "Latin brevis" (short), so the chain breaks logically. 4. The meaning of "briefcase" itself (a case for carrying documents) isn't explained by tracing only "brief" (short). I cannot write an accurate one-sentence etymology without a corrected chain that shows how both morphemes of "briefcase" developed, or clarification

briefcase (English): A case used for carrying documents, especially...

Definitions

  1. A case used for carrying documents, especially...

Ancestry of “briefcase”, step by step

briefcase traces back through two separate lines of ancestry.

via English Case

StepLanguageWordMeaning
1EnglishCaseabstract feature of a noun phrase that determines...
2GermanKäsecheese; nonsense
3Middle High Germankæsecheese
4Old High Germankāsicheese
5Proto-West Germanickāsīcheese
6Proto-Germanickāsijazcheese
7Latincāseuscheese
8Proto-Indo-Europeankwat-to ferment, become sour; to boil

via English brief

StepLanguageWordMeaning
1EnglishbriefOf short duration; happening quickly; Concise;...
2Middle Englishbrefconcise; brief; diminutive, little
3Old Frenchbriefbrief, short in length; letter or statement
4Latinbrevisshort, small, little, narrow; brief, short;...
5Proto-Italic*breɣʷis
6Proto-Indo-Europeanmréǵʰusshort; brief
7Proto-Indo-Europeanmreǵʰ-short

Words derived from “briefcase

Every word from Proto-Indo-European kwat-