refactor: remove callback thisArg support

docs/rxjs-next/COMPATIBILITY.md

@@ -400,10 +400,12 @@ whether the RxJS form delegates, which additional functionality it supplies,
 and which behavior or types intentionally differ. It must also prove that
 installing the Symbol does not alter the platform method.
 
-The P2.4 `map` pilot is the first recorded overlap. `observable[map](project,
-thisArg?)` owns an RxJS projection index and optional callback receiver,
-constructs through the RxJS `[create]` protocol, and participates in the
-platform layer's shared activation lifecycle. It does not delegate to
+The P2.4 `map` pilot is the first recorded overlap. `observable[map](project)`
+owns an RxJS projection index, constructs through the RxJS `[create]` protocol,
+and participates in the platform layer's shared activation lifecycle. D-059
+removes the inherited RxJS 7 callback-receiver argument from this and every
+other RxJS Next callback API; migration uses a closure or
+`Function.prototype.bind`. The Symbol form does not delegate to
 `observable.map(project)`, and installing it leaves that platform-owned string
 method unchanged. Focused and native/fallback kernel tests cover both the
 additional Symbol behavior and non-interference.

docs/rxjs-next/DECISIONS.md

@@ -476,7 +476,7 @@ Status meanings:
 
 ## D-023 — Keep RxJS map and filter overloads on exact Symbol keys
 
-- **Status:** Accepted
+- **Status:** Superseded by D-059
 - **Decision:** The RxJS `map` and `filter` contracts are installed only under
   their exported exact Symbol keys. Their RxJS forms preserve the projection
   or predicate index and optional `thisArg`; `filter` also preserves Boolean
@@ -492,6 +492,10 @@ Status meanings:
   distinction for `filter`. Projection and predicate errors terminate the
   shared operator activation. Concurrent observers share one upstream
   activation and one index sequence under the platform lifecycle.
+- **Reason superseded:** RxJS Next removes callback `thisArg` parameters rather
+  than carrying this RxJS 7 convenience into the new API. Closures and
+  `Function.prototype.bind` express the same receiver capture without forcing
+  every operator notification through `Function.prototype.call`.
 
 ## D-024 — Let finite take cancel synchronous upstream work before its limit
 
@@ -1491,3 +1495,21 @@ Status meanings:
   operational and bootstrap costs for the current sole-maintainer release.
 - **Scope:** Stable `9.0.0`, promotion to `latest`, and future reconsideration
   of registry-supported trusted publishing remain separate decisions.
+
+## D-059 — Remove callback `thisArg` parameters from RxJS Next
+
+- **Status:** Accepted
+- **Decision:** RxJS Next callback APIs do not accept a separate `thisArg`.
+  Remove the parameter and receiver-aware overloads from Symbol-keyed `every`,
+  `filter`, `find`, `findIndex`, `map`, and static `partition`. Invoke their
+  predicates and projectors directly.
+- **Rationale:** A closure or `Function.prototype.bind` expresses an intentional
+  receiver at the call site. Retaining `thisArg` forces RxJS to dispatch every
+  value through `.call`, adding API and hot-path implementation cost for a
+  redundant convenience inherited from RxJS 7.
+- **Consequence:** Migration must rewrite a second callback-receiver argument
+  to a closure or bound function. The callback value/index/source arguments,
+  type-guard and Boolean-constructor overloads, cancellation, result
+  construction, and platform string-named methods are unchanged. Historical
+  RxJS 7 evidence retains its source identity, while active migrated specs use
+  closures or bound functions instead of asserting the removed overload.

docs/rxjs-next/OPEN_QUESTIONS.md

@@ -108,13 +108,14 @@ Decide per overlapping operator:
 - documentation that prevents false parity claims;
 - native and fallback evidence that the platform method remains untouched.
 
-P2.4 settles the pilot `map` case. The exact RxJS Symbol form supplies the
-RxJS projection index and optional `thisArg`, constructs through `[create]`,
-and follows the platform layer's shared activation contract. It does not
-delegate to or replace the string-named platform `map`; native and fallback
-kernel evidence verifies that the original method and descriptor remain
-unchanged. Other overlapping operators still require the same per-capability
-record before they are restored.
+P2.4 settled the pilot `map` overlap and D-059 later removed its inherited
+RxJS 7 callback-receiver argument. The exact RxJS Symbol form supplies the
+RxJS projection index, constructs through `[create]`, and follows the platform
+layer's shared activation contract. It does not delegate to or replace the
+string-named platform `map`; native and fallback kernel evidence verifies that
+the original method and descriptor remain unchanged. Other overlapping
+operators still require the same per-capability record before they are
+restored.
 
 ### 6. What is the canonical extension implementation pattern?
 

docs/rxjs-next/PROJECT_PLAN.md

@@ -80,9 +80,11 @@ wrappers in favor of direct D-037 `[create]` calls and recorded a further
 bundle-size reduction. P6.8 completed durable pull-request and `master` CI
 ownership for every accepted RxJS 9 test and release check. P6.9 implemented
 truthful status signals and security automation and validated their first live
-GitHub results. The user has now prioritized P6.10: one understandable,
-interactive single-maintainer beta publication command with npm two-factor
-authentication and no CI publishing credential.
+GitHub results. The user then explicitly prioritized P6.11, which removed
+inherited callback `thisArg` parameters and their hot-path dispatch cost. P6.10
+remains the sole `NEXT` item: one understandable, interactive single-maintainer
+beta publication command with npm two-factor authentication and no CI
+publishing credential.
 
 RxJS 9 and `9.0.0-beta.0` are selected under D-007. D-053 defines runtime,
 browser, bundler, channel, and RxJS 7 maintenance policy. Dates and staffing
@@ -1569,6 +1571,7 @@ names.
 | `DONE` | P6.8  | Complete RxJS 9 CI coverage and validate the resulting pull-request workflow matrix   |
 | `DONE` | P6.9  | Validate the first live dependency-review and Scorecard runs on GitHub                |
 | `NEXT` | P6.10 | Publish and verify the first beta with the interactive release command                |
+| `DONE` | P6.11 | Remove inherited callback `thisArg` parameters and direct-call callback hot paths     |
 
 #### P6.9 completion bar
 
@@ -1647,6 +1650,41 @@ review`. This completes P6.9; the later P6.10 ruleset migration must preserve
   OTP/WebAuthn publication, package-access hardening, registry verification,
   and the immutable GitHub Release remain required before `DONE`.
 
+#### P6.11 completion bar
+
+- Every RxJS Next callback API is audited for a separate `thisArg`; the exact
+  affected API inventory is recorded.
+- Receiver-aware overloads, implementation parameters, and `.call` dispatch
+  are removed from all affected APIs without changing platform-polyfill
+  receiver binding required by Web IDL and iterator protocols.
+- Focused and migrated tests no longer assert library-provided callback
+  receivers; source-pinned RxJS 7 identifiers remain historical evidence, and
+  active replacements demonstrate closures or `Function.prototype.bind`.
+- Focused source, migrated cold/polyfill, public type, package, kernel,
+  migration-document freshness, lint, and diff gates pass.
+
+#### P6.11 completion evidence
+
+- Audited RxJS production source and found exactly six APIs with a separate
+  callback receiver argument: Symbol-keyed `every`, `filter`, `find`,
+  `findIndex`, and `map`, plus static Symbol-keyed `partition`. Removed every
+  receiver-aware overload, implementation parameter, and callback `.call`.
+- Replaced active receiver assertions with ordinary value/index/source tests,
+  closures, or explicitly bound callbacks. Added public declaration checks
+  that reject the removed second or third arguments. Classified all six
+  source-pinned RxJS 7 cases as intentional divergences and made their
+  executable migrated programs bind callbacks instead of exercising the
+  removed overload.
+- Passed all 750 RxJS source tests, the 76 affected cold and 76 affected
+  polyfill migrated tests, lint with zero errors, public types, package build,
+  migration-document freshness, 97-Symbol installation, and all package import
+  fixtures. Exact complete audits retained the reviewed 2,299/39 cold and
+  2,316/22 polyfill outcomes.
+- Passed the eight-case packaged fallback/native Chrome 150 kernel contract.
+  The release performance gate measured approximately 63.0 million map values
+  and 140,627 cancellations per second. Marked P6.11 `DONE`; the completed
+  execution queue has no `NEXT` marker.
+
 #### P6.1 completion bar
 
 - All release packages share the accepted RxJS 9 prerelease identity and exact
@@ -3680,3 +3718,19 @@ conformance implementation depends on a runnable harness.
   remains the sole `NEXT` item until the command publishes and verifies
   `9.0.0-beta.0`, package access disallows automation tokens, and the immutable
   GitHub Release is recorded.
+### 2026-08-05 — P6.11 callback receiver removal
+
+- Audited the complete RxJS production source and removed callback `thisArg`
+  overloads and `.call` dispatch from `every`, `filter`, `find`, `findIndex`,
+  `map`, and `partition`; no platform-polyfill protocol receiver binding was
+  changed.
+- Reworked focused and migrated tests to use ordinary closures or bound
+  callbacks, added negative public-type assertions, and classified the six
+  source-pinned RxJS 7 receiver cases as intentional divergences while
+  preserving their historical IDs.
+- Passed 750 source tests, both 76-test affected migrated suites, exact complete
+  cold/polyfill audit baselines, public types, lint, package/build/import and
+  migration freshness gates, the packaged fallback/native Chrome kernel, and
+  the release performance floor.
+- Recorded D-059, marked P6.11 `DONE`, and retained P6.10 as the sole `NEXT`
+  item.