Fix hsthrift build (internal + OSS)

Summary:
## Summary

This diff fixes two related build issues for hsthrift:

1. **Internal build failure**: The Glean Haskell indexer was failing with `Unstructured annotations are not allowed: 'haxl.batched'`
2. **OSS build failure**: The GitHub CI build was/will be failing because thrift annotation files couldn't be found

### Background

The `math.thrift` file previously used an unstructured annotation:
```thrift
oneway void putMany(1: list<i64> val) (haxl.batched);
```

This was fixed by a codemod in **October 2025** (D83550305) which converted it to a structured annotation. However, that fix was **reverted in November 2025** (D86966535) by Simon Marlow because it broke the GitHub CI - the `thrift/annotation/thrift.thrift` file wasn't accessible in the OSS build environment.

The revert commit message stated:
> *"This broke github CI. The file `thrift/annotations/thrift.thrift` is not present in the hsthrift github repo, and this thrift file is just a test."*

Since then, enforcement of the unstructured annotation ban has become stricter in fbsource, causing the internal Glean Haskell indexer to fail (see Sandcastle workflow [508906757907574458](https://www.internalfb.com/sandcastle/workflow/508906757907574458)).

Additionally, in early **March 2026**, codemods ran across fbsource adding `include "thrift/annotation/thrift.thrift"` to other files in hsthrift that are compiled during the OSS build:
- `tests/if/hs_test.thrift` (March 2, 2026)
- `tests/if/foo.thrift` (March 2, 2026)
- `tests/if/constants.thrift`
- `tests/if/map.thrift`

This means the OSS build is now broken regardless of whether `math.thrift` is fixed - other files also need the annotation include path.

### The Fix

**1. `lib/test/if/math.thrift`** - Convert unstructured to structured annotation:
```thrift
include "thrift/annotation/thrift.thrift"
...
thrift.DeprecatedUnvalidatedAnnotations{items = {"haxl.batched": "1"}}
oneway void putMany(1: list<i64> val);
```

**2. `Makefile`** - Add include path for fbthrift annotation files:
```makefile
HSTHRIFT_PREFIX ?= $(HOME)/.hsthrift
THRIFT_INCLUDE := -I $(HSTHRIFT_PREFIX)/include
```

Then use `$(THRIFT_INCLUDE)` in the `thrift-cpp` target when invoking `thrift1`.

When fbthrift is installed via `new_install_deps.sh` to `~/.hsthrift/`, the thrift compiler can now find the annotation files at `~/.hsthrift/include/thrift/annotation/thrift.thrift`.

### Why this fixes both issues

- **Internal build**: Uses the structured annotation syntax that the Thrift compiler now requires
- **OSS build**: The Makefile now passes `-I ~/.hsthrift/include` to `thrift1`, allowing it to find `thrift/annotation/thrift.thrift` which is installed as part of fbthrift

Reviewed By: malanka, aahanaggarwal

Differential Revision: D96733254

fbshipit-source-id: 13c480f9a4cd11fc8ce4c2211fd47808e6046a99

Author: Catherine Gasnier

Makefile

@@ -7,6 +7,10 @@ CABAL_BIN := cabal
 THRIFT1 := thrift1
 CABAL := $(CABAL_BIN) $(CABAL_CONFIG_FLAGS) $(GETDEPS_CABAL_FLAGS)
 
+# Include path for fbthrift annotation files (installed by new_install_deps.sh)
+HSTHRIFT_PREFIX ?= $(HOME)/.hsthrift
+THRIFT_INCLUDE := -I $(HSTHRIFT_PREFIX)/include
+
 # Targets in this file invoke Cabal and hence can't be built in parallel
 .NOTPARALLEL:
 
@@ -122,13 +126,13 @@ thrift-hs:: compiler
 
 thrift-cpp::
 	mkdir -p cpp-channel/if cpp-channel/test/if
-	cd lib && $(THRIFT1) -I . --gen mstch_cpp2 \
+	cd lib && $(THRIFT1) $(THRIFT_INCLUDE) -I . --gen mstch_cpp2 \
 		-o ../cpp-channel/if \
 		if/RpcOptions.thrift
-	cd lib/test/if && $(THRIFT1) -I . --gen mstch_cpp2 \
+	cd lib/test/if && $(THRIFT1) $(THRIFT_INCLUDE) -I . --gen mstch_cpp2 \
                 -o ../../../cpp-channel/test/if \
                 math.thrift
-	cd tests/if && $(THRIFT1) -I . --gen mstch_cpp2 \
+	cd tests/if && $(THRIFT1) $(THRIFT_INCLUDE) -I . --gen mstch_cpp2 \
 		-o . \
 		hs_test.thrift
 

lib/test/if/math.thrift

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+include "thrift/annotation/thrift.thrift"
+
 package "facebook.com/hs/thrift/test"
 
 namespace cpp2 "cpp2"
@@ -30,7 +32,8 @@ service Calculator extends Adder {
 
   oneway void put(1: i64 val);
 
-  oneway void putMany(1: list<i64> val) (haxl.batched);
+  @thrift.DeprecatedUnvalidatedAnnotations{items = {"haxl.batched": "1"}}
+  oneway void putMany(1: list<i64> val);
 
   i64 get();