Small and medium-sized enterprises in developing economies operate within a complex interplay of institutional constraints and entrepreneurial action. The specific mechanisms through which firms navigate these challenges to build resilience remain inadequately understood, particularly in sub-Saharan African contexts. This study aims to diagnose the determinants of firm-level resilience by analysing the dynamic relationship between structural constraints and entrepreneurial agency. It seeks to identify the most salient business challenges and the adaptive strategies firms employ to sustain operations. A sequential explanatory mixed-methods design was employed. First, a longitudinal analysis of firm-level panel data was conducted. This was followed by in-depth, semi-structured interviews with founders and senior managers to contextualise the quantitative trends. Quantitative analysis revealed a significant positive association between strategic networking and revenue stability during periods of macroeconomic volatility. Thematic analysis of interview data identified 'improvisational bricolage'—the creative recombination of scarce resources—as a central mechanism for overcoming acute liquidity constraints, cited by over 70% of respondents. Firm resilience is not merely a function of external structures or internal agency alone, but is co-produced through iterative, adaptive practices. Entrepreneurial action effectively reconfigures, but does not eliminate, systemic constraints. Policymakers should design support programmes that enhance firms' capacity for strategic networking and resource improvisation. Financial institutions ought to develop diagnostic tools that assess adaptive capability, not just static financial health. resilience, entrepreneurial agency, structural constraints, mixed methods, SMEs, business diagnostics This paper provides a novel diagnostic framework that integrates longitudinal quantitative metrics with rich qualitative evidence to unpack the co-constitutive dynamics of constraint and agency in firm survival.