Framed the migration as a challenge, not a replacement. The language mattered. This wasn't "we're replacing your component." It was "this is the hardest technical migration on the roadmap, and you're the only person who can lead it." That reframe was genuine — the lead developer's knowledge of the existing system's edge cases was irreplaceable. The migration would be faster and safer with them driving it than with anyone else.

Gave them real ownership of the strategy. They chose the porting approach. They designed the test harness. They approved compatibility changes. They mentored others on the component's behavior. This wasn't delegated busywork — it was genuine technical authority over how the migration would execute. When someone controls the strategy, they have skin in its success rather than incentive to prove it was premature.

Built guardrails that protected quality without micromanaging. Four rules defined the engagement. No big-bang rewrites — adapter or sidecar first, native rewrite later. Dual-run validation with automatic fallback — the new system runs alongside the old, and any mismatch triggers a safe rollback. A change freeze on new features, gated by RFCs, to prevent scope creep disguised as improvement. And a 90-day timebox that created urgency without pressure — a challenge with a finish line.

Structured the work as a 30/60/90 with measurable milestones. At 30 days: adapter built, golden-master test harness running, canary deployment with fallback, 95% fixture parity. At 60 days: extended coverage, dual-run validation in staging, draft documentation, two weeks of clean dual-run data. At 90 days: production cutover, begin native optimization, documentation and training complete with two trained deputies.

Made the work visible. The lead developer's contribution to the migration was surfaced in sprint reviews, credited in release communications, and linked to their performance goals. Not as a formal incentive program — just as the natural consequence of doing important, difficult work. When the organization sees the migration as a technical achievement rather than a maintenance chore, the person driving it is recognized by default.

Addressed the bus factor without threatening their importance. The lead developer's deep knowledge was an asset, but it was also a single point of failure. Pairing sessions, trained deputies, and mandatory documentation were built into the 90-day plan — framed as "your expertise is too valuable to exist in one person's head," not as reducing dependency. Same outcome, opposite emotional response.