fix(core): preserve runtime transport contract

[jrusso1020]

What

Preserve the createRuntimePlayer transport contract through the public window.__player object.

Why

Runtime initialization replaced player methods after construction and dropped seek keepPlaying semantics.

How

Remove the post-construction method replacement and test the actual public player at integer and fractional frame rates.

Test plan

• core runtime player/init tests; producer runtime-browser contract
• Stack-wide lint, format, build, typecheck, and relevant integration gates

[jrusso1020]

• refactor(repo): resolve changed-code audit #2174
• test(engine): isolate peer abort regression #2173
• refactor(cli): decompose render phases #2172
• refactor(cli): centralize process lifecycle #2171
• fix(cloudrun): publish adapter contract #2170
• test(repo): execute packed subpaths #2169
• refactor(repo): centralize package subpaths #2168
• refactor(core): own edit protocol contract #2167
• test(compiler): enforce preview render parity #2166
• refactor(studio): gate SDK operation families #2165
• refactor(studio): gate Acorn writer migration #2164
• refactor(producer): make capture plans immutable #2163
• refactor(producer): unify render requests #2162
• refactor(engine): type capture failures #2161
• refactor(engine): manage child process lifecycles #2160
• refactor(engine): add fingerprinted browser leases #2159
• refactor(render): centralize execution ownership #2158
• refactor(core): unify composition contract #2157
• fix(studio): enforce optimistic file concurrency #2156
• fix(studio): make sdk cutover transactional #2155
• fix(render): publish artifacts atomically #2154
• fix(render): surface structured outcomes #2153
• fix(player): own connection and media resources #2152
• fix(core): preserve runtime transport contract #2151 👈 (View in Graphite)
• fix(player): version runtime protocol #2150
• test(repo): verify packed consumers #2149
• test(repo): enforce workspace contracts #2148
• fix(core): enforce strict runtime safety #2147
• test(producer): gate source tests by execution lane #2146
• fix(core): make timing masks safe for source loaders #2145
• chore(repo): forbid tracked generated artifacts #2144
• main

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[miguel-heygen]

Incremental-boundary review at b720c3f5 (the parent protocol PR remains separately gated by my #2150 finding).

• packages/core/src/runtime/init.ts:2114-2220 constructs the final clock-backed transport once and preserves the complete seek(..., { keepPlaying }) contract instead of replacing public methods after construction.
• packages/core/src/runtime/player.ts:136-151 keeps the factory-owned method identities stable while delegating to that transport.
• The real public-player browser test covers 24/30/60/29.97 fps, and local focused verification passed: Core player/init 91/91 plus Producer runtime-browser 6/6.

No new findings in this PRs own diff.

— Magi / deepwork

Verdict: APPROVE
Reasoning: The transport extraction removes the post-construction override hazard and restores keepPlaying semantics with focused unit and real-browser coverage.

The base branch was changed.